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 A185233 #23 Dec 28 2024 22:00:38
%S A185233 5,14,27,39,65,54,104,125,242,209,374,459,350,275,714,782,350,1155,
%T A185233 1224,1022,1425,840,594,1715,1700,1869,702,1260,1224,1014,2645,2430,
%U A185233 3185,1127,4094,3317,1274,5124,6060,3834,3059,6174,5565,7749,8349,7395,7344
%N A185233 A185129(n) is the a(n)-th triangular number.
%C A185233 See A185128 for further information.
%D A185233 Albert H. Beiler, Recreations in the theory of numbers, New York, Dover, (2nd ed.) 1966, p. 197, no. 8.
%H A185233 N. J. A. Sloane, <a href="/A185128/a185128.jpg">Annotated scan of Beiler's Table 81</a>, based on page 197 of Beiler's "Recreations in the Theory of Numbers: The Queen of Mathematics Entertains", New York, Dover, First ed., 1964.
%e A185233 A185122(2) = 105 which is the 14th triangular number, so a(2) = 14.
%o A185233 (PARI) lista(nn) = {v = vector(nn, n, n*(n+1)/2); for (n=2, nn, for (k=1, n-1, if (ispolygonal(v[n]+v[k], 3) && ispolygonal(v[n]-v[k], 3), print1(k, ", "));););} \\ _Michel Marcus_, Jan 08 2015
%Y A185233 Cf. A000217, A185128, A185129, A185223, A185243, A185253, A185257, A185258.
%K A185233 nonn
%O A185233 1,1
%A A185233 _Martin Renner_, Jan 20 2012
%E A185233 Edited (with a simpller definition) by _N. J. A. Sloane_, Dec 28 2024