# Triangular number

Triangular numbers: a(n) = C(n+1,2) = n(n+1)/2 = 0+1+2+...+n.

0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351, 378, 406, 435, 465, 496, 528, 561, 595, 630, 666, 703, 741, 780, 820, 861, 903, 946, 990, 1035, 1081, 1128, 1176, 1225, 1275, 1326, 1378, 1431, ...

A SQUANGULAR number is a number that is simultaneously triangular and square.
The first few are : 1, 36, 1225, 41616, 1413721, 48024900, 1631432881, 55420693056, 1882672131025, ...

# Pentagonal number

Pentagonal numbers: n(3n-1)/2 :

0, 1, 5, 12, 22, 35, 51, 70, 92, 117, 145, 176, 210, 247, 287, 330, 376, 425, 477, 532, 590, 651, 715, 782, 852, 925, 1001, 1080, 1162, 1247, 1335, 1426, 1520, 1617, 1717, 1820, 1926, 2035, 2147, 2262, 2380, 2501, 2625, 2752, 2882, 3015, 3151, ...

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Question: Can you find a number that is simultaneously triangular, square and pentagonal?
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