OFFSET
1,1
COMMENTS
Conjecture: For n > 1, if a(n) = n concatenated with k then k < n^2.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(5) = 521, as 51,56,511 and 516 are all composite.
MAPLE
f:= proc(n) local k, p;
for k from 1 by n do
p:= n*10^(1+ilog10(k))+k;
if isprime(p) then return p fi
od
end proc:
map(f, [$1..100]); # Robert Israel, Jan 13 2017
PROG
(PARI) a(n)=my(t); forstep(k=1, oo, n, if(isprime(t=10^#digits(k)*n+k), return(t))) \\ Charles R Greathouse IV, Jan 13 2017
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Dec 16 2003
EXTENSIONS
More terms from David Wasserman, Feb 14 2006
STATUS
approved