Digit-reassembly number

Digit-reassembly numbers, or Osiris numbers, are numbers that are equal to the sum of permutations of sub-samples of their own digits (compare the dismemberment and reconstruction of the god Osiris in Egyptian mythology). For example, 132 = 12 + 21 + 13 + 31 + 23 + 32.

Simple examples

In base ten, the smallest Osiris numbers are these, with a number-length of three digits and digit-span of two for the permutated sums:

132 = 12 + 21 + 13 + 31 + 23 + 32

264 = 24 + 42 + 26 + 62 + 46 + 64

396 = 36 + 63 + 39 + 93 + 69 + 96

A larger Osiris number in base ten is this, with a number-length of five digits and digit-span of three for the permutated sums:

35964 = 345 + 354 + 435 + 453 + 534 + 543 + 346 + 364 + 436 + 463 + 634 + 643 + 349 + 394 + 439 + 493 + 934 + 943 + 356 + 365 + 536 + 563 + 635 + 653 + 359 + 395 + 539 + 593 + 935 + 953 + 369 + 396 + 639 + 693 + 936 + 963 + 456 + 465 + 546 + 564 + 645 + 654 + 459 + 495 + 549 + 594 + 945 + 954 + 469 + 496 + 649 + 694 + 946 + 964 + 569 + 596 + 659 + 695 + 956 + 965

Maximal Osiris numbers

If 0 is treated as a full digit in all positions, then 207 in base ten is a maximal Osiris number, being equal to the sum of all possible distinct numbers formed from permutated sub-samples of its digits:

207 = 2 + 0 + 7 + 20 + 02 + 27 + 72 + 07 + 70

In other bases, maximal Osiris numbers exist that do not contain zeros. For example:

253₉ = 2 + 3 + 5 + 23 + 32 + 25 + 52 + 35 + 53 (base = 9)

210 = 2 + 3 + 5 + 21 + 29 + 23 + 47 + 32 + 48 (base = 10)

276₁₃ = 2 + 6 + 7 + 26 + 62 + 27 + 72 + 67 + 76 (b=13)

435 = 2 + 6 + 7 + 32 + 80 + 33 + 93 + 85 + 97 (b=10)

DF53₁₇ = 3 + 5 + D + F + 35 + 53 + 3D + D3 + 3F + F3 + 5D + D5 + 5F + F5 + DF + FD + 35D + 3D5 + 53D + 5D3 + D35 + D53 + 35F + 3F5 + 53F + 5F3 + F35 + F53 + 3DF + 3FD + D3F + DF3 + F3D + FD3 + 5DF + 5FD + D5F + DF5 + F5D + FD5 (b=17)

68292 = 3 + 5 + 13 + 15 + 56 + 88 + 64 + 224 + 66 + 258 + 98 + 226 + 100 + 260 + 236 + 268 + 965 + 1093 + 1509 + 1669 + 3813 + 3845 + 967 + 1127 + 1511 + 1703 + 4391 + 4423 + 1103 + 1135 + 3823 + 4015 + 4399 + 4559 + 1681 + 1713 + 3857 + 4017 + 4433 + 4561 (b=10)

Multi-minimal Osiris numbers

Using the same terminology, 132, 264 and 396 are minimal Osiris numbers, being equal to the sums of all numbers formed from permutated samples of only two of their digits. 35964 is also minimal, sampling three digits, but 34658 is a multi-minimal Osiris number, being equal to the sums of all numbers formed from permutated samples of one or three of its digits:

34658 = 3 + 4 + 5 + 6 + 8 + 345 + 354 + 435 + 453 + 534 + 543 + 346 + 364 + 436 + 463 + 634 + 643 + 348 + 384 + 438 + 483 + 834 + 843 + 356 + 365 + 536 + 563 + 635 + 653 + 358 + 385 + 538 + 583 + 835 + 853 + 368 + 386 + 638 + 683 + 836 + 863 + 456 + 465 + 546 + 564 + 645 + 654 + 458 + 485 + 548 + 584 + 845 + 854 + 468 + 486 + 648 + 684 + 846 + 864 + 568 + 586 + 658 + 685 + 856 + 865

30659 and 38657 are similarly multi-minimal, using permutated samples of one and three of their digits.

Tests for Osiris numbers

Testing for Osiris numbers is simplified when one notes that, for example, each digit of 132 occurs twice in the ones and tens position of the sums:

132 = 12 + 21 + 13 + 31 + 23 + 32 = 2x11 + 2x22 + 2x33 = 22 + 44 + 66

The test can be further simplified:

132 = 2 x (11 + 22 + 33) = 2 x (1 + 2 + 3) x 11 = 2 x 6 x 11

If only numbers with unique non-zero digits are considered, a three-digit number in base ten can have a digit-sum ranging from 6 = 1+2+3 to 24 = 7+8+9. If these potential digit-sums are plugged into the formula 2 x digit-sum x 11, the digit-sum of the result will determine whether or not the result is an Osiris number.

1. 2 x 6 x 11 = 132.

2. Digit-sum(132) = 1 + 2 + 3 = 6.

3. Therefore 132 is an Osiris number.

1. 2 x 7 x 11 = 154.

2. Digit-sum(154) = 1 + 5 + 4 = 10.

3. Therefore 154 is not an Osiris number.

In 35964, each digit occurs 12 times in the ones, tens and hundreds position of the sums:

35964 = 12x333 + 12x444 + 12x555 + 12x666 + 12x999 = 3996 + 5328 + 6660 + 7992 + 11988

35964 = 12 x (333 + 444 + 555 + 666 + 999) = 12 x (3 + 4 + 5 + 6 + 9) x 111 = 12 x 27 x 111

The test for further five-digit Osiris numbers of the same form (sub-sampling three digits) will use potential digit-sums between 15 = 1+2+3+4+5 and 35 = 5+6+7+8+9. However, only 35964 has a digit-sum equal to the digit-sum tested in the formula.

See also

• Digit sum