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%I #7 Feb 23 2015 23:20:28
%S 0,1,3,6,10,136,231,300,3160,3741,4371,5565,5995,6328,6555,10011,
%T 10440,10731,13366,13530,14196,18528,19900,20301,21115,23220,25200,
%U 25651,30135,30628,30876,32385,34716,37401,42778,43071,46971,47278,53301,60031,60378,63903,64620,69378,74691,86320,89253,90525
%N Triangular numbers n with digits d_1, d_2, ..., d_k such that d_1*(d_1+1)/2 + ... + d_k*(d_k+1)/2 is a triangular number.
%o (PARI) istri(n)=for(k=0,n+1,if(k*(k+1)/2==n,return(1)));0
%o for(n=0,10^3,N=n*(n+1)/2;d=digits(N);s=0;for(i=1,#d,s+=d[i]*(d[i]+1)/2);if(istri(s),print1(N,", ")))
%Y Cf. A000217, A254956.
%K nonn,base
%O 1,3
%A _Derek Orr_, Feb 11 2015