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

1,2

Links

Table of n, a(n) for n=1..69.

Prog

(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

Crossrefs

Cf. A168007, A168009.

Sequence in context: A133021 A131208 A353467 * A178810 A319627 A334990

Adjacent sequences: A168005 A168006 A168007 * A168009 A168010 A168011

Keyword

sign

Author

Omar E. Pol, Nov 19 2009

Extensions

More terms from Jinyuan Wang, Mar 14 2020

Status

approved