A368075 a(n) is the least n-gonal number that can be expressed as the difference of two positive n-gonal numbers in exactly n ways.
15, 144, 10045, 21945, 220077, 99008
Offset: 3
Examples
a(3) = 15: 15 = 21 - 6 = 36 - 21 = 120 - 105.
Links
- Eric Weisstein's World of Mathematics, Polygonal Number
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