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
Robert Israel, Table of n, a(n) for n = 1..65
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
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