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a(n) is the smallest number which can be represented as the sum of two distinct nonzero octagonal numbers in exactly n ways, or -1 if no such number exists.
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%I #27 Jun 30 2024 22:12:09

%S 9,1053,12641,68141,365641,953181,2830641,6232341,13969041,23211261,

%T 104733741,84994021,175873641,159851141,538547641,602713041,810204416,

%U 1019740041,1053265741,1972957241,3339356041,5914492241,6886737541,6388758241,8902368041,7858982841,4942246941,18439299341,26639916441

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

%H Michael S. Branicky, <a href="/A374143/b374143.txt">Table of n, a(n) for n = 1..38</a>

%H Michael S. Branicky, <a href="/A374141/a374141.txt">Python program for A374141, A374142, and A374143</a>

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

%e a(2) = 1053 = 8 + 1045 = 408 + 645.

%o (Python) # see linked program

%Y Cf. A000567, A093195, A332989, A342326, A374141, A374142.

%K nonn

%O 1,1

%A _Ilya Gutkovskiy_, Jun 28 2024

%E a(9)-a(29) from _Michael S. Branicky_, Jun 29 2024