login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A226957 Number of prime divisors p of 2n such that p-1 divides n. 2
1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

MATHEMATICA

fa = FactorInteger; a[n_] := Sum[If[IntegerQ[n/(fa[2 n][[i, 1]]-1)], 1, 0], {i, Length[fa[2 n]]}]; Table[a[n], {n, 1, 100}]

PROG

(PARI) a(n)=my(f=factor(2*n)[, 1]); sum(i=1, #f, n%(f[i]-1)==0) \\ Charles R Greathouse IV, Jun 26 2013

CROSSREFS

Sequence in context: A262618 A107577 A073700 * A108775 A300826 A305936

Adjacent sequences:  A226954 A226955 A226956 * A226958 A226959 A226960

KEYWORD

nonn

AUTHOR

José María Grau Ribas, Jun 24 2013

EXTENSIONS

Erroneous a(87) added by T. D. Noe, corrected by Charles R Greathouse IV, Jun 26 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 15 21:31 EST 2019. Contains 329151 sequences. (Running on oeis4.)