OFFSET
2,4
COMMENTS
a(n) = 1 if and only if A080378(n-1) = 2. - Robert Israel, Feb 07 2018
LINKS
Robert Israel, Table of n, a(n) for n = 2..10000
FORMULA
MAPLE
seq(padic:-ordp(ithprime(n)*ithprime(n-1)-1, 2), n=2..200); # Robert Israel, Feb 07 2018
PROG
(PARI) a(n) = valuation(prime(n)*prime(n-1) - 1, 2); \\ Michel Marcus, Sep 30 2013
(Python)
from sympy import prime
def A023520(n): return (~(m:=prime(n)*prime(n-1)-1)& m-1).bit_length() # Chai Wah Wu, Jul 07 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset set to 2 and a(2) corrected by Michel Marcus, Sep 30 2013
STATUS
approved