OFFSET
1,4
LINKS
Kevin P. Thompson, Table of n, a(n) for n = 1..106
Florian Luca and Igor E. Shparlinski, On the largest prime factor of n! + 2^n - 1, Journal de Théorie des Nombres de Bordeaux 17 (2005), 859-870.
FORMULA
EXAMPLE
a(6) = 2 since n! + 2^n - 1 = 6! + 2^6 - 1 = 783 = 3^3 * 29 has 2 distinct prime factors.
MATHEMATICA
a = {}; Do[AppendTo[a, n! + 2^n - 1], {n, 1, 40}]; b = {}; Do[c = Length[FactorInteger[a[[n]]]]; AppendTo[b, c], {n, 1, Length[a]}]; b
PrimeNu @ Table[n! + 2^n - 1, {n, 1, 30}] (* Amiram Eldar, Feb 05 2020 *)
PROG
(PARI) a(n)=omega(n!+2^n-1) \\ Charles R Greathouse IV, Feb 01 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Apr 06 2008, corrected Apr 22 2008
EXTENSIONS
a(1) - a(40) verified and a(41)- a(75) added by Klaus Brockhaus, Nov 19 2009
a(76)-a(81) from Amiram Eldar, Feb 05 2020
a(82) onwards from Kevin P. Thompson, Jun 29 2022
STATUS
approved