A337834 If k is the n-th number ending in 1,3,7, or 9, a(n) is the least prime > k ending in k.

11, 13, 17, 19, 211, 113, 317, 419, 421, 223, 127, 229, 131, 233, 137, 139, 241, 443, 347, 149, 151, 353, 157, 359, 461, 163, 167, 269, 271, 173, 277, 179, 181, 283, 487, 389, 191, 193, 197, 199, 5101, 1103, 5107, 1109, 2111, 2113, 1117, 3119, 3121, 1123, 4127, 1129, 2131, 4133, 2137, 4139, 2141

Offset

1,1

Comments

a(n) exists by Dirichlet's theorem on primes in arithmetic progressions.

Links

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

Index entries for primes involving decimal expansion of n

Example

For n=3 the third number ending in 1,3,7 or 9 is 7 and the least prime > 7 ending in 7 is a(3)=17.
For n=12 the 12th number ending in 1,3,7 or 9 is 29 and the least prime > 29 ending in 29 is a(12)=229.

Maple

f:= proc(n) local d, x;
  d:= ilog10(n)+1;
  for x from n + 10^d by 10^d do
    if isprime(x) then return x fi
  od
end proc:
map(f, [seq(seq(10*i+j, j=[1, 3, 7, 9]), i=0..99)];

Crossrefs

Cf. A085821, A338715.

Sequence in context: A327349 A240899 A090149 * A089691 A036979 A036977

Adjacent sequences: A337831 A337832 A337833 * A337835 A337836 A337837

Keyword

nonn,base

Author

Robert Israel, Sep 24 2020

Status

approved