login
A087345
Smallest prime which is a concatenation of n successive triangular numbers, or 0 if no such number exists.
2
3, 13, 210231253, 171190210231, 36101521, 136101521, 1596165317111770183018911953, 105120136153171190210231, 0, 17020172051739117578177661795518145183361852818721
OFFSET
1,1
COMMENTS
a(9k) = 0 because the concatenation of 9k successive triangular numbers is always divisible by 3. - David Wasserman, May 10 2005
a(66) > 10^999 if it is not 0.- Robert Israel, Mar 13 2018
LINKS
EXAMPLE
a(3)=210231253 because 210231253 is the smallest prime formed by concatenation of 3 consecutive triangular numbers i.e. 210,231 and 253.
MAPLE
ccat:= proc(L) local r, x;
r:= L[1];
for x in L[2..-1] do
r:= r*10^(1+ilog10(x))+x
od:
r
end proc:
f:= proc(n) local k, j, t;
if n mod 9 = 0 then return 0 fi;
for k from 1 do
t:= ccat([seq(j*(j+1)/2, j=k..k+n-1)]);
if isprime(t) then return t fi
od
end proc:
map(f, [$1..20]); # Robert Israel, Mar 13 2018
CROSSREFS
Cf. A087344.
Sequence in context: A092830 A317481 A271393 * A048756 A174211 A264611
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Sep 06 2003
EXTENSIONS
Corrected and extended by Shyam Sunder Gupta, Apr 25 2005 and David Wasserman, May 10 2005
Edited by N. J. A. Sloane, Sep 02 2010
STATUS
approved