A057019 Difference between n!! and the first prime after n!! + 1.

2, 3, 2, 3, 2, 5, 2, 5, 2, 7, 4, 11, 16, 11, 8, 17, 4, 19, 64, 17, 2, 17, 2, 13, 8, 71, 2, 61, 4, 19, 118, 59, 32, 23, 82, 19, 178, 41, 4, 101, 8, 41, 4, 59, 16, 47, 16, 131, 298, 29, 64, 31, 16, 83, 194, 31, 2, 41, 298, 53, 316, 193, 8, 67, 334, 53, 32, 43, 226, 149, 386, 37

Offset

1,1

Comments

Analogous to the Fortunate numbers, but unlike them, not all terms here are prime. Many odd-indexed terms are powers of two and all even-indexed terms are prime.

Links

Table of n, a(n) for n=1..72.

Mathematica

NextPrime[ n_Integer ] := (k=n+1; While[ !PrimeQ[ k ], k++ ]; Return[ k ]); f[ n_Integer ] := (p = n!! + 1; q = NextPrime[ p ]; Return[ q - p + 1 ]); Table[ f[ n ], {n, 1, 75} ]
dfnp[n_]:=Module[{df=n!!}, NextPrime[df+1]-df]; Array[dfnp, 80] (* Harvey P. Dale, Mar 25 2012 *)

Prog

(MuPAD) for n from 1 to 72 do f := n!!:a := nextprime(f+2)-f:print(a) end_for; // Zerinvary Lajos, Feb 22 2007

Crossrefs

Cf. A006882, A057034.

Sequence in context: A046215 A256113 A256368 * A084740 A229708 A204895

Adjacent sequences: A057016 A057017 A057018 * A057020 A057021 A057022

Keyword

nonn

Author

Robert G. Wilson v, Sep 09 2000

Status

approved