A064147 Numbers k such that k! - 1 and k! + 1 have the same number of divisors, i.e., tau(k! - 1) = tau(k! + 1).

3, 8, 10, 13, 17, 20, 22, 24, 26, 34, 39, 53, 59, 61, 63, 69, 70, 76, 80, 87, 97, 99, 103, 124, 130

Offset

1,1

Comments

200 and 392 are also terms.

236 and 634 are terms. - Chai Wah Wu, Jan 03 2020

Links

Table of n, a(n) for n=1..25.

Paul Leyland, Generalized Cullen and Woodall numbers

Andrew Walker, N!+/-1 Factoring Page

Prog

(PARI) {A064147(n)=if(numdiv(n!-1)==numdiv(n!+1), n, 0)}

Crossrefs

Cf. A000005.

Sequence in context: A226641 A212966 A074186 * A287573 A122529 A137920

Adjacent sequences: A064144 A064145 A064146 * A064148 A064149 A064150

Keyword

nonn,more

Author

Vladeta Jovovic, Sep 11 2001

Extensions

More terms from Randall L Rathbun, Jan 11 2002

a(23)-a(25) from Chai Wah Wu, Jan 03 2020

Status

approved