A073693 Product of next n odd numbers plus 2 is prime.

1, 1, 1, 4, 1, 1, 2, 2, 1, 1, 5, 1, 3, 10, 1, 1, 2, 1, 4, 1, 2, 2, 8, 3, 2, 2, 6, 3, 2, 1, 12, 2, 1, 3, 4, 1, 1, 7, 4, 1, 2, 1, 2, 6, 3, 6, 2, 1, 1, 7, 19, 26, 5, 2, 3, 1, 81, 3, 56, 28, 23, 2, 2, 17, 1, 6, 4, 9, 1, 2, 4, 1, 5, 9, 1, 7, 3, 1, 2, 16, 1, 6, 49, 7, 1, 2, 6, 3, 1, 6, 17, 3, 1

Offset

0,4

Comments

Group the odd numbers so that the product of the terms in each group + 2 is a prime: (1), (3), (5), (7, 9, 11, 13), (15), (17), (19, 21), (23, 25), (27), (29), ...; sequence gives the number of terms in each group.

Links

Table of n, a(n) for n=0..92.

Mathematica

t = {}; s = 1; c = 0; Do[s = s*i; c += 1; If[PrimeQ[s + 2], AppendTo[t, c]; s = 1; c = 0], {i, 1, 1200, 2}]; t (* Jayanta Basu, Jul 07 2013 *)

Prog

(PARI) o=1:for(k=1, 100, n=1:p=o:while(!isprime(p+2), o=o+2:p=p*o:n=n+1):o=o+2:print1(n", "))

Crossrefs

Cf. A073691, A073692.

Sequence in context: A077604 A112985 A293769 * A360916 A360918 A100261

Adjacent sequences: A073690 A073691 A073692 * A073694 A073695 A073696

Keyword

nonn

Author

Amarnath Murthy, Aug 12 2002

Extensions

Corrected and extended by Ralf Stephan, Mar 18 2003

Status

approved