A202448 Least k such that k*n!! +1 is a prime number.

1, 1, 2, 2, 2, 2, 2, 2, 8, 2, 10, 3, 2, 6, 10, 3, 2, 2, 14, 5, 10, 9, 6, 2, 22, 10, 4, 2, 26, 2, 22, 3, 8, 11, 30, 11, 6, 4, 2, 15, 52, 10, 22, 13, 10, 9, 34, 11, 18, 18, 2, 10, 26, 12, 4, 34, 4, 18, 26, 16, 34, 25, 22, 12, 14, 32, 50, 24, 4, 8, 12, 14, 26, 4

Offset

1,3

Links

Table of n, a(n) for n=1..74.

Example

a(9) = 8 because 8*9!! + 1 = 8*945 + 1 = 7561 is prime.

Mathematica

Table[k = 0; While[!PrimeQ[k*n!! +1], k++]; k, {n, 85}]

Crossrefs

Cf. A006882.

Sequence in context: A139813 A172009 A299150 * A339165 A129381 A319991

Adjacent sequences: A202445 A202446 A202447 * A202449 A202450 A202451

Keyword

nonn

Author

Michel Lagneau, Dec 19 2011

Status

approved