A229262 Smallest triangular number whose decimal expansion ends (nontrivially) with the n-th triangular number.

21, 153, 36, 210, 2415, 3321, 528, 136, 2145, 3655, 666, 378, 1891, 6105, 205120, 185136, 10153, 399171, 63190, 78210, 364231, 5253, 210276, 180300, 11325, 406351, 1378, 81406, 357435, 4465, 215496, 18528, 12561, 413595, 57630, 84666, 65703, 3741, 220780

Offset

1,1

Links

Chai Wah Wu, Table of n, a(n) for n = 1..10000 (terms 1..200 from Shyam Sunder Gupta)

Example

a(4)=210 because 210 is the smallest triangular number that ends with 4th triangular number i.e. 10.

Mathematica

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}]

Crossrefs

Cf. A000217.

Sequence in context: A239569 A219599 A221694 * A184376 A184368 A078396

Adjacent sequences: A229259 A229260 A229261 * A229263 A229264 A229265

Keyword

nonn,base

Author

Shyam Sunder Gupta, Sep 17 2013

Status

approved