|
Search: id:A054989
|
|
|
| A054989 |
|
Number of prime divisors of -1 + (product of first n primes). |
|
+0
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
(list; graph; listen)
|
|
|
OFFSET
|
1,4
|
|
|
LINKS
|
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}]]
|
|
CROSSREFS
|
Cf. A000040 (prime numbers), A001359 (twin primes). Also A054988, A054990, A054991, A054992.
Sequence in context: A113136 A156267 A160325 this_sequence A051631 A073725 A055223
Adjacent sequences: A054986 A054987 A054988 this_sequence 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 (rgwv(AT)rgwv.com), Mar 24 2001
|
|
|
Search completed in 0.002 seconds
|
