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

1,1

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

Cf. A068695.

Sequence in context: A030675 A110786 A059642 * A344175 A126330 A090506

Adjacent sequences: A090917 A090918 A090919 * A090921 A090922 A090923

Keyword

base,nonn

Author

Amarnath Murthy, Dec 16 2003

Extensions

More terms from David Wasserman, Feb 14 2006

Status

approved