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 A116980 #7 Oct 05 2020 10:34:12
%S A116980 1,1,1,0,0,0,0,0,0,1,1,4,19,23,16,43,59,66,127,492,886,964,2595,11426,
%T A116980 36780,78070,131232,423402,1302893,3356226,6673924,16604441,32195439,
%U A116980 69328860
%N A116980 Number of ways to arrange integers 1...n so that the sum of each adjacent pair is a triangular number, not counting reversals.
%e A116980 a(9)=1, since {3,7,8,2,4,6,9,1,5} and its reversal are the only permutations
%e A116980 of 1..9 with the given property. Here 3+7, 7+8, 8+2, 4+6, 6+9, 9+1 and 1+5 are all triangular numbers.
%Y A116980 Cf. A051239.
%K A116980 nonn
%O A116980 0,12
%A A116980 _Giovanni Resta_, Apr 01 2006
%E A116980 a(29)-a(33) from _Donovan Johnson_, Aug 27 2010
%E A116980 a(0)=1 prepended by _Alois P. Heinz_, Oct 05 2020