A383485 a(n) = 2*(2*(n - 1)! + n + 2) mod (n*(n + 2)).

1, 4, 3, 12, 5, 16, 0, 20, 31, 24, 11, 28, 0, 32, 49, 36, 17, 40, 0, 44, 67, 48, 0, 52, 54, 56, 85, 60, 29, 64, 0, 68, 70, 72, 109, 76, 0, 80, 121, 84, 41, 88, 0, 92, 139, 96, 0, 100, 102, 104, 157, 108, 0, 112, 114, 116, 175, 120, 59, 124, 0, 128, 130, 132, 199, 136, 0, 140

Offset

1,2

Comments

Fixed points are the lesser of twin primes A001359.

Positions of zeros are primes p such that p + 2 is not a prime A067774.

Links

Andrew Howroyd, Table of n, a(n) for n = 1..10000

Formula

a(A001359(n)) = n.

a(A067774(n)) = 0.

Mathematica

Table[Mod[2(2(n - 1)! + n + 2), n(n + 2)], {n, 68}]

Prog

(PARI) a(n) = 2*(2*(n - 1)! + n + 2) % (n*(n + 2)) \\ Andrew Howroyd, Nov 20 2025

Crossrefs

Cf. A073830, A001359, A067774, A005563.

Sequence in context: A121844 A091512 A106285 * A240134 A193800 A061727

Adjacent sequences: A383482 A383483 A383484 * A383486 A383487 A383488

Keyword

nonn

Author

Giorgos Kalogeropoulos, Apr 28 2025

Status

approved