A092679 Numbers k such that 3*2^k has only one anti-divisor.

0, 1, 5, 17

Offset: 1

Author

Lior Manor, Mar 03 2004

Keywords

• nonn
• hard
• more

Comments

Next term should be greater than 3*10^6 (cf. A181490).

See A066272 for definition of anti-divisor.

Crossrefs

Cf. A066466, A092680, A181490.

Programs

Python

A092679 = [i for i,n in enumerate(map(lambda x:3*2**x,range(20))) if len([d for d in range(2,n,2) if n%d and not 2*n%d]+[d for d in range(3,n,2) if n%d and 2*n%d in [d-1,1]])==1] # Chai Wah Wu, Aug 09 2014

Formula

A092680(n) = 3*2^a(n).

a(n) = A181490(n) - 1. - Max Alekseyev, Feb 14 2025