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A054989 Number of prime divisors of -1 + (product of first n primes). 9
0, 1, 1, 2, 1, 1, 2, 3, 3, 2, 2, 4, 1, 2, 3, 3, 2, 3, 3, 2, 2, 4, 3, 1, 2, 2, 4, 4, 4, 3, 3, 3, 3, 3, 3, 4, 4, 4, 5, 3, 5, 4, 5, 4, 4, 4, 4, 2, 3, 3, 2, 4, 3, 4, 2, 4, 4, 7, 4, 3, 3, 4, 4, 3, 3, 1, 3, 1, 4, 3, 5, 5, 4, 4, 6, 5, 5, 3, 4, 3, 4, 4, 3, 4, 2, 3, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..99

Hisanori Mishima, Factorizations of many number sequences

R. G. Wilson v, Explicit factorizations

EXAMPLE

a(4)=2 because 2*3*5*7 - 1 = 209 = 11*19

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}]]

PrimeOmega[#] & /@ (FoldList[Times, Prime[Range[81]]] - 1) (* Harvey P. Dale, Mar 11 2017 *)

CROSSREFS

Cf. A054988, A054990, A054991, A054992.

Sequence in context: A113136 A156267 A160325 * A051631 A073725 A055223

Adjacent sequences:  A054986 A054987 A054988 * A054990 A054991 A054992

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(42)-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 18:30 EST 2020. Contains 332082 sequences. (Running on oeis4.)