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A305670 Numbers k not ending in zero that are a substring of k*(k+1). 3


%S 9,99,146,999,3701,8881,9999,10512,13088,13271,13466,15625,49547,

%T 50502,60146,73398,85941,99999,155613,205062,513335,712539,999999,

%U 1005012,1060146,1334666,3990487,5005002,9999999,20050062,26930824,39341318,46022544,58331666,63116013

%N Numbers k not ending in zero that are a substring of k*(k+1).

%C A002283 is a subset of this sequence.

%C Contains 5*10^(2*m)+5*10^m+2 and 2*10^(2*m+1)+5*10^(m+1)+62 for m >= 2. - _Robert Israel_, Jun 29 2018

%H Giovanni Resta, <a href="/A305670/b305670.txt">Table of n, a(n) for n = 1..90</a>

%e 13088 * 13089 = 171308832;

%e 13271 * 13272 = 176132712.

%p P:=proc(q) local k,n; for n from 1 to q do if n mod 10>0 then

%p for k from 1 to ilog10(n*(n+1))-ilog10(n)+1 do

%p if n=trunc(n*(n+1)/10^(k-1)) mod 10^(ilog10(n)+1) then print(n);

%p break; fi; od; fi; od; end: P(10^8);

%Y Cf. A002283, A316263.

%K nonn,base

%O 1,1

%A _Paolo P. Lava_, Jun 28 2018

%E Edited by _Robert Israel_, Jun 29 2018

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Last modified December 12 20:12 EST 2019. Contains 329961 sequences. (Running on oeis4.)