A163981 -id:A163981 - cp's OEIS frontend

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

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

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.

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

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

Cf. A029707, A071680, A163981, A342027.

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]);

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

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

cp's OEIS Frontend

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

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