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 A187744 #17 Jul 13 2013 12:03:48 %S A187744 0,1,3,6,10,12,15,19,21,24,28,30,33,37,42,46,51,55,60,64,69,73,78,82, %T A187744 87,91,96,100,102,105,109,111,114,118,120,123,127,132,136,141,145,150, %U A187744 154,159,163,168,172,177,181,186,190,195,201,204,208,210,213,217 %N A187744 Numbers whose digital sum is a triangular number. %C A187744 Every term with some permutations can become another term of this sequence. %C A187744 The subsequence of primes begins: 3, 19, 37, 73, 91, 127... %C A187744 The subsequence of triangular numbers begins: 1, 3, 6, 10, 15, 21, 28, 55... %H A187744 Reinhard Zumkeller, <a href="/A187744/b187744.txt">Table of n, a(n) for n = 1..10000</a> %F A187744 If decimal expansion of n is x1 x2 ... xk then x1 + x2 + ... xk = T. %F A187744 A010054(A007953(a(n))) = 1. - _Reinhard Zumkeller_, Jan 03 2013 %t A187744 TriangularQ[n_] := IntegerQ[Sqrt[1 + 8 n]]; Select[Range[0, 300], TriangularQ[Total[IntegerDigits[#]]] &] (* _T. D. Noe_, Jan 03 2013 *) %o A187744 (Haskell) %o A187744 a187744 n = a187744_list !! (n-1) %o A187744 a187744_list = filter ((== 1) . a010054 . a007953) [0..] %o A187744 -- _Reinhard Zumkeller_, Jan 03 2013 %Y A187744 Cf. A000217, A007960, A000027. %K A187744 nonn,base %O A187744 1,3 %A A187744 _Dario Piazzalunga_, Jan 03 2013