A168008 First differences of A168007.

1, 2, -1, 3, -1, 5, -1, 3, -1, 11, -1, 3, -1, 23, -1, 3, -1, 47, -1, 3, -1, 5, -1, 3, -1, 101, -1, 3, -1, 7, -1, 11, -1, 3, -1, 13, -1, 233, -1, 3, -1, 467, -1, 3, -1, 5, -1, 3, -1, 941, -1, 3, -1, 7, -1, 1889, -1, 3, -1, 3779, -1, 3, -1, 7559, -1, 3, -1, 13, -1

Offset: 1

Author

Omar E. Pol, Nov 19 2009

Keywords

• sign

Crossrefs

Cf. A168007, A168009.

Programs

Python

from itertools import count, islice
from sympy import primefactors
def A168008_gen(): # generator of terms
    a = 1
    for n in count(2):
        yield (b:=min(primefactors(a),default=1) if a&1 or a==2 else -1)
        a += b
A168008_list = list(islice(A168008_gen(),20)) # Chai Wah Wu, Mar 14 2023

Extensions

More terms from Jinyuan Wang, Mar 14 2020