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%I #6 Sep 19 2013 12:06:22
%S 21,153,36,210,2415,3321,528,136,2145,3655,666,378,1891,6105,205120,
%T 185136,10153,399171,63190,78210,364231,5253,210276,180300,11325,
%U 406351,1378,81406,357435,4465,215496,18528,12561,413595,57630,84666,65703,3741,220780
%N Smallest triangular number whose decimal expansion ends (nontrivially) with the n-th triangular number.
%H Shyam Sunder Gupta, <a href="/A229262/b229262.txt">Table of n, a(n) for n = 1..200</a>
%e a(4)=210 because 210 is the smallest triangular number that ends with 4th triangular number i.e. 10.
%t TriangularQ[n_Integer?Positive] := IntegerQ[Sqrt[8*n + 1]]; f[n_] := (k = 1; While[a = ToExpression[ ToString[k] <> ToString[n]]; ! TriangularQ[a], k++ ]; a); Table[f[ n*(n + 1)/2], {n, 1, 50}]
%Y Cf. A000217.
%K nonn,base
%O 1,1
%A _Shyam Sunder Gupta_, Sep 17 2013
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