A229235 Smallest triangular numbers whose decimal expansion begins (nontrivially) with n-th triangular number.

15, 36, 66, 105, 153, 2145, 2850, 3655, 4560, 5565, 666, 7875, 9180, 10585, 12090, 13695, 153181, 1711, 190653, 210276, 231540, 253116, 276396, 3003, 325221, 351541, 378885, 406351, 435711, 4656, 496506, 528906, 561270, 595686, 6303025, 666435, 703891

Offset

1,1

Links

Shyam Sunder Gupta, Table of n, a(n) for n = 1..500

Example

a(4)=105 because 105 is triangular number that begins with 4th triangular number i.e. 10.

Mathematica

TriangularQ[n_Integer?Positive] := IntegerQ[Sqrt[8*n + 1]]; q = {}; Do[x = n*(n + 1)/2; Do[a = IntegerLength[m]; c = x*10^a + m; If[TriangularQ[c], AppendTo[q, c]; Break[]], {m, 1, 10000}], {n, 1, 100}]; q

Crossrefs

Cf. A000217.

Sequence in context: A033709 A067707 A166146 * A346881 A293156 A329909

Adjacent sequences: A229232 A229233 A229234 * A229236 A229237 A229238

Keyword

base,nonn

Author

Shyam Sunder Gupta, Sep 17 2013

Status

approved