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 A117404 #9 Dec 26 2014 12:49:33 %S A117404 0,1,10,36,45,153,171,351,630,1035,1431,2016,3240,3321,4005,8001, %T A117404 10440,13041,13203,16110,21321,23220,25200,67896,89676,101025,105111, %U A117404 114003,186966,187578,198765,222111,239778,279378,292995,299925,320400,321201 %N A117404 Triangular numbers for which the sum of the digits is a square. %H A117404 Harvey P. Dale, <a href="/A117404/b117404.txt">Table of n, a(n) for n = 1..10000</a> %e A117404 45 is in the sequence because (1) it is a triangular number and (2) the sum of its digits 4+5=9 is a square. %t A117404 Select[Accumulate[Range[0,1000]],IntegerQ[Sqrt[Total[IntegerDigits[ #]]]]&] (* _Harvey P. Dale_, Dec 26 2014 *) %o A117404 (PARI) isok(n) = ispolygonal(n, 3) && issquare(sumdigits(n)); \\ _Michel Marcus_, Feb 26 2014 %Y A117404 Cf. A000217. %K A117404 base,nonn %O A117404 1,3 %A A117404 Luc Stevens (lms022(AT)yahoo.com), Apr 26 2006 %E A117404 Corrected by _Michel Marcus_, Feb 26 2014