A343908 - OEIS

A343908

a(n) is the least prime == 4 (mod prime(n)).

2, 7, 19, 11, 37, 17, 89, 23, 73, 149, 97, 41, 127, 47, 239, 163, 181, 431, 71, 359, 223, 83, 419, 271, 101, 307, 107, 967, 113, 569, 131, 397, 1237, 421, 2239, 457, 1103, 167, 839, 523, 541, 547, 577, 197, 1777, 601, 1481, 227, 3863, 233, 3499, 2633, 727, 757, 1289, 1319, 811, 1901, 281, 1409

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

EXAMPLE

a(3) = 19 because 19 is the least prime == 4 (mod prime(3)).

a(4) = 11 because 11 is the least prime == 4 (mod prime(4)).

MAPLE

a:= proc(n) local q, p; p:= ithprime(n); q:= p;

do if irem(q-4, p)=0 then break fi;

q:= nextprime(q);

od; q

end:

seq(a(n), n=1..60); # Alois P. Heinz, May 03 2021

MATHEMATICA

s = {}; p = 5; Do[q = p + 2; While[Mod[q, p] != 4, q = NextPrime[q]]; AppendTo[s, q]; p = NextPrime[p], {100}]; s

PROG

(PARI) a(n) = my(p=prime(n)); forprime(q=2, , if (Mod(q, p) == 4, return(q))); \\ Michel Marcus, May 03 2021

CROSSREFS

Cf. A000040, A023200 (primes p such that p+4 is also prime), A034694, A035095, A279756.

Sequence in context: A368593 A218684 A337614 * A100408 A259370 A103034

Adjacent sequences: A343905 A343906 A343907 * A343909 A343910 A343911

KEYWORD

nonn

AUTHOR

Zak Seidov, May 03 2021

STATUS

approved