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