Triangular number
A triangular number is a number that is the sum of all of the natural numbers up to a certain number. For example, 10 is a triangular number because 1 + 2 + 3 + 4 = 10. The first 25 triangular numbers are:0̸͕̤̫̉̽̚͝,̷̩͍͉̬̑ ̶̯͒͌1̷̡͇̻̞̓͒̎,̶̙͌ ̷͉̻̄͋̊3̸̠̱̿,̸̛̱̟͖̿̈́ ̴͇̳̖̫̓͛́͝6̸̩̚,̵̛̙̼̈̕ ̷̠̲͆͠1̵͔̀̒0̵̭̝̖̔͝ͅ,̴̧͈̹͉̎̾ ̶̩́1̵̧̢̫͓̏5̶̐̑͝ͅ,̶̡̛̖͖̣̿ ̷̱̳̔͒̂2̵̯̱̺̊̊̓͜1̸͔̤̮͋,̴̳̞͍̖̀ ̵̪̝̇2̷͔̰̩͛ͅ8̷̟̇̑,̶̲̓͠ ̵̘͔̱̅3̶̨͛ͅ6̸͇̻͂͆͝,̴͕̞͂̓͒ ̷̲̟̗̐̔4̵͔̋͗͗5̵͙͚̍̍̐͛͜,̶̛̭͗͗ ̴̮̼͑̓̔5̷̜̰̻͛͌̓͘5̸̟̖̽̅͐̕͜,̸̟̪̬̅̍͐ ̴̢̭̼̹̆6̴̫̭͗̌ͅ6̴̛̝̇̂́,̴̨̳̠̾̀͠ ̶͓́̑͌7̸͚̰̯̇8̷̢̠̱͍̋́,̶͖̔̾̚͜͜͜͝ ̷̝̎̾͗̃9̷͙̪̹́̾1̷̖̝̈́͗͆͜,̵͓̤̱̞̒̈́͊̚ ̸̗̺̹̌͝1̸͈͖̲̌0̵̢̟̝͗5̵̨̝̟̔,̶͓̄͋͒͘ ̶̜̜̄͜͝1̸̡̩͔̀2̷̪̣̠͋̕0̷͍̋̏̚,̸̰̱͈͆̇ ̶̥̘̬͑͐̓̕1̵͈̅3̴͎̹͖̳́͊6̶̭̅͑̐,̸̪̑̉͘ ̷͛̕͜ͅ1̵̪̽̀͑5̷̠̞͋̚3̷͔̞͒̏̾,̵̩̐̏͛ ̷̯̣͌1̶̡͖̦̋͜͝7̴̫̫͍͕͑̽1̴̣̔̎̃̒,̸̧̟̬̅̌̾ ̴̦̭̘̠̎1̴͖̟͊̈́͝9̷͈̎̄̂̚ͅ0̵͙͙͖͝,̴̮̤̯̮͌ ̶̡̰͑2̷̢̼̳̾͆1̶͙̩̻͂̋0̸̲͌̈̀,̸̪̒̄͝ ̴͕͑2̷͚̠̄3̵̦̦̤͒̈̄1̴͈͇̠̝͑̐̌,̷̢̤̣̿̾͑͂ ̴̰̊̃ͅ2̶̱̼͔̞̑̅5̴̙̟̖̇͝3̷̼̂,̵̢̬͚̀̑͋ ̶͕̥̝͝2̵̣̻͋̍7̷̢̺̥͂͂6̷̟̉,̷̫̬̍̄̌͜ ̸͓͔͕̗͛́3̶̨̙̏̿0̶͔̺͍̪̅́͠0̸̩̖̦̈́.̶̢̝͓̩͝͝͠
A triangular number is calculated by the equation: .
