A060778 a(n) = gcd(tau(n+1), tau(n)), where tau = A000005.

1, 2, 1, 1, 2, 2, 2, 1, 1, 2, 2, 2, 2, 4, 1, 1, 2, 2, 2, 2, 4, 2, 2, 1, 1, 4, 2, 2, 2, 2, 2, 2, 4, 4, 1, 1, 2, 4, 4, 2, 2, 2, 2, 6, 2, 2, 2, 1, 3, 2, 2, 2, 2, 4, 4, 4, 4, 2, 2, 2, 2, 2, 1, 1, 4, 2, 2, 2, 4, 2, 2, 2, 2, 2, 6, 2, 4, 2, 2, 5, 1, 2, 2, 4, 4, 4, 4, 2, 2, 4, 2, 2, 4, 4, 4, 2, 2, 6, 3, 1, 2, 2, 2, 8, 4

Offset: 1

Author

Labos Elemer, Apr 26 2001

Keywords

• nonn

Links

• Harry J. Smith, Table of n, a(n) for n=1..1000

Crossrefs

Cf. A000005, A057921, A058074.

Programs

Mathematica

GCD@@@Partition[DivisorSigma[0,Range[110]],2,1] (* Harvey P. Dale, May 27 2014 *)

PARI

a(n) = gcd(numdiv(n), numdiv(n+1)); \\ Michel Marcus, Jan 12 2018

Python

from math import gcd
from sympy import divisor_count
def A060778(n): return gcd(divisor_count(n+1),divisor_count(n)) # Chai Wah Wu, Aug 12 2023

Formula

a(n) = gcd(A000005(n+1), A000005(n)).