

A337834


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


3



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
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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

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



