A117309 - OEIS

%I #11 Jun 28 2014 11:49:34

%S 0,1,6,10,15,78,105,231,276,465,528,780,861,1176,1275,1653,1770,2211,

%T 2346,2850,3003,3570,3741,4371,4560,5253,5460,5995,6216,6441,7260,

%U 7503,11175,12246,12561,14028,14878,15225,17205,17578,20301,20706,22155,24090

%N Triangular numbers for which the sum of the digits is a hexagonal number.

%H Harvey P. Dale, <a href="/A117309/b117309.txt">Table of n, a(n) for n = 0..1000</a>

%e 105 is in the sequence because (1) it is a triangular number and (2) the sum of its digits 1+0+5=6 is a hexagonal number.

%t Join[{0},Select[Accumulate[Range[350]],IntegerQ[(1+Sqrt[8Total[ IntegerDigits[#]]+1])/4]&]] (* _Harvey P. Dale_, Jun 06 2011 *)

%Y Cf. A000217, A000384.

%K base,nonn

%O 0,3

%A Luc Stevens (lms022(AT)yahoo.com), Apr 26 2006

%E Corrected and extended by _Harvey P. Dale_, Jun 06 2011