A341284 a(n) is the least prime == -prime(n) (mod 2*prime(n+1)).

7, 23, 37, 41, 89, 59, 73, 151, 157, 43, 127, 131, 239, 59, 419, 307, 73, 359, 367, 401, 419, 1163, 881, 307, 311, 967, 547, 569, 3697, 397, 691, 419, 457, 757, 163, 821, 839, 179, 1259, 907, 2111, 967, 1777, 599, 223, 3803, 3863, 2063, 3499, 1201, 3617, 2269, 263, 269, 1889, 2441, 283, 1409

Offset

2,1

Comments

a(k) is the least odd prime == -prime(k) (mod prime(k+1)).

a(k) = A163981(k) if and only if k is not in A029707.

a(k) = 2*prime(k+1)-prime(k) if and only if prime(k+1) is in A071680.

Links

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

Formula

(a(k) + prime(k)) mod (2*prime(k+1)) = 0.

Example

a(3) = 23 is the least prime == -5 (mod 14), where prime(3) = 5 and prime(4) = 7.

Maple

f:= proc(n) local k;
  for k from 2*ithprime(n+1)-ithprime(n) by 2*ithprime(n+1)  do
    if isprime(k) then return k fi
  od;
end proc:
map(f, [$2..100]);

Prog

(PARI) a(n) = forprime(p=2, , if (Mod(p, 2*prime(n+1)) == -prime(n), return (p))); \\ Michel Marcus, Feb 25 2021

Crossrefs

Cf. A029707, A071680, A163981, A342027.

Sequence in context: A275777 A329931 A157811 * A227421 A098029 A098039

Adjacent sequences: A341281 A341282 A341283 * A341285 A341286 A341287

Keyword

nonn,look

Author

J. M. Bergot and Robert Israel, Feb 25 2021

Status

approved