A374144 - OEIS

A374144

a(n) is the smallest number which can be represented as the sum of two distinct nonzero n-gonal numbers in exactly n ways, or -1 if no such number exists.

%I #13 Feb 16 2025 08:34:07

%S 81,1105,205427,483031,9402323,6232341,79324200,768459127,2265692766,

%T 2413112833,6737406626,150437989675,45319359337,15140186701

%N a(n) is the smallest number which can be represented as the sum of two distinct nonzero n-gonal numbers in exactly n ways, or -1 if no such number exists.

%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PolygonalNumber.html">Polygonal Number</a>

%H Michael S. Branicky, <a href="/A374144/a374144.py.txt">Python program for A374144</a>

%e a(3) = 81 = 3 + 78 = 15 + 66 = 36 + 45.

%o (Python) # see linked program

%Y Cf. A057145, A093195, A332989, A342326, A350405, A374141, A374142, A374143.

%K nonn,more,changed

%O 3,1

%A _Ilya Gutkovskiy_, Jun 28 2024

%E a(9)-a(16) from _Michael S. Branicky_, Jun 30 2024