

A073693


Product of next n odd numbers plus 2 is prime.


2



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
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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: A016525 A077604 A112985 * A100261 A016526 A247341
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



