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 A119238 Numbers k such that the decimal representation of k is contained as substring in that of the k-th triangular number. 2

%I

%S 1,5,19,25,199,625,1999,2102,5582,9376,9909,10100,16833,19999,41012,

%T 55741,74491,83885,88102,90625,151774,199999,201002,558257,626522,

%U 740312,798097,810062,890625,1001000,1030563,1668333,1999999,2646751

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

%H Giovanni Resta, <a href="/A119238/b119238.txt">Table of n, a(n) for n = 1..101</a> (terms < 10^12)

%p select(n->searchtext(convert(n, string), convert(n*(n+1)/2, string))>0, [\$0..10^5]); # _Paolo P. Lava_, Jun 27 2018

%t Select[Range@100000, ({}!=StringPosition[ToString[ #(#+1)/2], ToString@# ]) &]

%t 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 *)

%Y Cf. A046831.

%K base,nonn

%O 1,2

%A _Giovanni Resta_, May 10 2006

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Last modified December 2 17:48 EST 2021. Contains 349445 sequences. (Running on oeis4.)