A380421 - OEIS

A380421

a(n) is the inverse of 2^3 modulo prime(n).

2, 2, 1, 7, 5, 15, 12, 3, 11, 4, 14, 36, 27, 6, 20, 37, 23, 42, 9, 64, 10, 52, 78, 85, 38, 13, 67, 41, 99, 16, 82, 120, 87, 56, 19, 59, 102, 21, 65, 112, 68, 24, 169, 74, 25, 132, 28, 142, 86, 204, 30, 211, 157, 225, 33, 101, 34, 104, 246, 177, 110, 192, 39, 274

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

OFFSET

2,1

LINKS

Robert Israel, Table of n, a(n) for n = 2..10000

FORMULA

a(n) = 8^(-1) (mod prime(n)) for n >= 2.

a(n) = (A006254(n) * A292411(n)) (mod prime(n)) for n >= 2.

If prime(n) mod 8 = j in {1, 3, 5, 7}, then a(n) = (1 + (8-j)*prime(n))/8. - Robert Israel, Feb 24 2025

MAPLE

seq(1/8 mod ithprime(n), n=2..65); # Alois P. Heinz, Feb 14 2025

MATHEMATICA

a[n_] := ModularInverse[8, Prime[n]]; Array[a, 100, 2] (* Amiram Eldar, Feb 05 2025 *)

PROG

(PARI) a(n) = lift(1/Mod(8, prime(n))); \\ Michel Marcus, Jan 25 2025

(Python)

from sympy import prime

def A380421(n): return pow(8, -1, prime(n)) # Chai Wah Wu, Feb 14 2025

CROSSREFS

Cf. A006254, A292411.

Sequence in context: A021455 A271460 A248924 * A307455 A136502 A144502

Adjacent sequences: A380418 A380419 A380420 * A380422 A380423 A380424

KEYWORD

nonn,look

AUTHOR

R. J. Cintra, Jan 25 2025

STATUS

approved