A119238 Numbers k such that the decimal representation of k is contained as substring in that of the k-th triangular number.

1, 5, 19, 25, 199, 625, 1999, 2102, 5582, 9376, 9909, 10100, 16833, 19999, 41012, 55741, 74491, 83885, 88102, 90625, 151774, 199999, 201002, 558257, 626522, 740312, 798097, 810062, 890625, 1001000, 1030563, 1668333, 1999999, 2646751

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• base
• nonn

Links

• Giovanni Resta, Table of n, a(n) for n = 1..101 (terms < 10^12)

Crossrefs

Cf. A046831.

Programs

Mathematica

Select[Range@100000, ({}!=StringPosition[ToString[ #(#+1)/2], ToString@# ]) &]
Select[Range[3*10^6],SequenceCount[IntegerDigits[(#(#+1))/2], IntegerDigits[ #]]>0&] (* The program uses the SequenceCount function from Mathematica version 10 *) (* Harvey P. Dale, Dec 26 2015 *)