This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A199809 #41 Oct 21 2023 01:48:45 %S A199809 16,50,211,384,470,1053,1500,2242,3197,3277,5501,6780,8710,9896,10584, %T A199809 15198,15395,21237,23346,28696,33596,37725,40795,48474,55369,54146, %U A199809 69113,75732,84962,92541,95623,98672,123575,127317,146639,141066,154975,173416,201032 %N A199809 a(n) is the smallest number which is the sum of two positive n-gonal numbers in more than one way. %C A199809 The sequence is not monotonically increasing as a(27) = 55369 > 54146 = a(28). %H A199809 Chai Wah Wu, <a href="/A199809/b199809.txt">Table of n, a(n) for n = 3..2628</a> %e A199809 a(3)=16 since 16=1+15=6+10, such that 1,15,6,10 are all triangular numbers (A000217) and there are no other positive numbers less than 16 with such a property. %Y A199809 Cf. A000217. %K A199809 nonn %O A199809 3,1 %A A199809 _Vladimir Shevelev_, Dec 16 2013 %E A199809 More terms from _Peter J. C. Moses_, Dec 16 2013