A090920 Primes of the form n followed by the least k == 1 (mod n).

11, 23, 31, 41, 521, 61, 71, 89, 919, 101, 1123, 1213, 131, 1429, 151, 1697, 17137, 181, 191, 2081, 211, 2267, 2347, 241, 251, 26183, 271, 281, 29581, 3061, 311, 32257, 331, 3469, 3571, 3637, 37223, 3877, 39157, 401, 41411, 421, 431, 44221, 4591, 461, 47189

Offset: 1

Author

Amarnath Murthy, Dec 16 2003

Keywords

• base
• nonn

Comments

Conjecture: For n > 1, if a(n) = n concatenated with k then k < n^2.

Examples

			a(5) = 521, as 51,56,511 and 516 are all composite.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A068695.

Programs

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

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

Extensions

More terms from David Wasserman, Feb 14 2006