A349668 - OEIS

A349668

a(n) is the n-th safe prime reduced mod n.

0, 1, 2, 3, 2, 5, 6, 3, 5, 9, 7, 11, 9, 9, 8, 3, 3, 17, 12, 7, 5, 3, 12, 23, 8, 5, 26, 23, 2, 29, 3, 31, 2, 27, 9, 23, 20, 13, 11, 23, 8, 23, 39, 39, 14, 13, 12, 23, 23, 49, 14, 51, 40, 17, 2, 39, 17, 33, 28, 47, 42, 49, 32, 43, 34, 59, 58, 55, 11, 27, 42, 23

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

OFFSET

1,3

LINKS

Karl-Heinz Hofmann, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A005385(n) mod n.

a(n) = (2*A005384(n) + 1) mod n.

EXAMPLE

A005385(12) = 263; 263 == 11 mod 12.

MATHEMATICA

p = Select[Prime[Range[700]], PrimeQ[(# - 1)/2] &]; Mod[p, Range[Length[p]]] (* Amiram Eldar, Jan 10 2022 *)

PROG

(Python)

from sympy import isprime

n = 1

for p in range (2, 10000):

if isprime(p) and isprime(2*p+1):

print ((2*p+1)%n, end=", ")

n += 1

(PARI) lista(nn) = my(v=[x|x<-primes(nn), bigomega(x-1)==2]); vector(#v, k, v[k] % k); \\ Michel Marcus, Jan 10 2022

CROSSREFS

Cf. A005385 (safe primes), A005384 (Sophie Germain primes).

Sequence in context: A348066 A227071 A276270 * A214571 A135873 A070673

Adjacent sequences: A349665 A349666 A349667 * A349669 A349670 A349671

KEYWORD

nonn

AUTHOR

Karl-Heinz Hofmann, Jan 09 2022

STATUS

approved