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%I #13 Mar 13 2018 04:17:57
%S 3,13,210231253,171190210231,36101521,136101521,
%T 1596165317111770183018911953,105120136153171190210231,0,
%U 17020172051739117578177661795518145183361852818721
%N Smallest prime which is a concatenation of n successive triangular numbers, or 0 if no such number exists.
%C a(9k) = 0 because the concatenation of 9k successive triangular numbers is always divisible by 3. - _David Wasserman_, May 10 2005
%C a(66) > 10^999 if it is not 0.- _Robert Israel_, Mar 13 2018
%H Robert Israel, <a href="/A087345/b087345.txt">Table of n, a(n) for n = 1..65</a>
%e a(3)=210231253 because 210231253 is the smallest prime formed by concatenation of 3 consecutive triangular numbers i.e. 210,231 and 253.
%p ccat:= proc(L) local r,x;
%p r:= L[1];
%p for x in L[2..-1] do
%p r:= r*10^(1+ilog10(x))+x
%p od:
%p r
%p end proc:
%p f:= proc(n) local k,j,t;
%p if n mod 9 = 0 then return 0 fi;
%p for k from 1 do
%p t:= ccat([seq(j*(j+1)/2,j=k..k+n-1)]);
%p if isprime(t) then return t fi
%p od
%p end proc:
%p map(f, [$1..20]); # _Robert Israel_, Mar 13 2018
%Y Cf. A087344.
%K base,nonn
%O 1,1
%A _Amarnath Murthy_, Sep 06 2003
%E Corrected and extended by _Shyam Sunder Gupta_, Apr 25 2005 and _David Wasserman_, May 10 2005
%E Edited by _N. J. A. Sloane_, Sep 02 2010