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 A073690 Group the natural numbers so that the product of the terms in each group + 1 is a prime: (1), (2), (3, 4), (5, 6), (7, 8, 9, 10, 11), (12), (13, 14, 15), (16), ... This is the sequence of the number of terms in each group. 2
 1, 1, 2, 2, 5, 1, 3, 1, 2, 5, 2, 6, 7, 5, 3, 9, 3, 2, 3, 5, 2, 2, 5, 1, 6, 10, 13, 1, 11, 8, 3, 2, 3, 1, 7, 7, 18, 43, 7, 6, 7, 1, 27, 16, 1, 7, 6, 2, 1, 2, 16, 6, 9, 3, 2, 24, 3, 1, 6, 8, 6, 8, 6, 19, 6, 1, 12, 5, 7, 13, 1, 7, 3, 7, 6, 6, 1, 7, 20, 20, 20, 2, 1, 5, 1, 10, 3, 1, 7, 2, 1, 13, 1, 9, 9 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS 4 cannot be a member. Do all other positive integers occur? LINKS Table of n, a(n) for n=0..94. MATHEMATICA t = {}; s = 1; c = 0; Do[s = s*i; c += 1; If[PrimeQ[s + 1], AppendTo[t, c]; s = 1; c = 0], {i, 630}]; t (* Jayanta Basu, Jul 07 2013 *) CROSSREFS Cf. A073688, A073689. Sequence in context: A267857 A173169 A016586 * A079301 A079300 A128932 Adjacent sequences: A073687 A073688 A073689 * A073691 A073692 A073693 KEYWORD nonn AUTHOR Amarnath Murthy, Aug 12 2002 EXTENSIONS More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 24 2003 and Dean Hickerson, Apr 27 2003 STATUS approved

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Last modified September 22 01:06 EDT 2023. Contains 365503 sequences. (Running on oeis4.)