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A054988 Number of prime divisors of 1 + (product of first n primes). 7
1, 1, 1, 1, 1, 2, 3, 2, 2, 3, 1, 3, 3, 2, 3, 4, 4, 2, 2, 4, 2, 3, 2, 4, 3, 2, 4, 4, 3, 3, 5, 3, 6, 2, 3, 2, 5, 4, 4, 2, 6, 3, 4, 3, 5, 6, 7, 2, 6, 3, 5, 3, 4, 2, 6, 5, 4, 5, 3, 5, 5, 5, 3, 3, 5, 5, 6, 3, 4, 4, 7, 5, 3, 4, 1, 2, 5, 5, 5, 4, 5, 3, 5, 4, 6, 5, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Table of n, a(n) for n=1..87.

Hisanori Mishima, Factorizations of many number sequences

R. G. Wilson v, Explicit factorizations

EXAMPLE

a(6)=2 because 2*3*5*7*11*13+1 = 30031 = 59 * 509

MATHEMATICA

a[q_] := Module[{x, n}, x=FactorInteger[Product[Table[Prime[i], {i, q}][[j]], {j, q}]+1]; n=Length[x]; Sum[Table[x[[i]][[2]], {i, n}][[j]], {j, n}]]

CROSSREFS

Cf. A054989, A054990, A054991, A054992.

Sequence in context: A270026 A128049 A104543 * A143393 A269111 A166497

Adjacent sequences:  A054985 A054986 A054987 * A054989 A054990 A054991

KEYWORD

nonn,hard

AUTHOR

Arne Ring (arne.ring(AT)epost.de), May 30 2000

EXTENSIONS

More terms from Robert G. Wilson v, Mar 24 2001

a(44)-a(81) from Charles R Greathouse IV, May 07, 2011

a(82)-a(87) from Amiram Eldar, Oct 03 2019

STATUS

approved

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Last modified February 20 14:58 EST 2020. Contains 332078 sequences. (Running on oeis4.)