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A305444 a(n) = Product_{p is odd and prime and divisor of n} (p - 2). 3
1, 1, 1, 1, 3, 1, 5, 1, 1, 3, 9, 1, 11, 5, 3, 1, 15, 1, 17, 3, 5, 9, 21, 1, 3, 11, 1, 5, 27, 3, 29, 1, 9, 15, 15, 1, 35, 17, 11, 3, 39, 5, 41, 9, 3, 21, 45, 1, 5, 3, 15, 11, 51, 1, 27, 5, 17, 27, 57, 3, 59, 29, 5, 1, 33, 9, 65, 15, 21, 15, 69, 1, 71, 35, 3, 17 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Denominator of c_n = Product_{odd p| n} (p-1)/(p-2). Numerator is A173557. [Yamasaki and Yamasaki]. - N. J. A. Sloane, Jan 19 2020

LINKS

Markus Sigg, Table of n, a(n) for n = 1..10000

Yamasaki, Yasuo, and Aiichi Yamasaki, On the Gap Distribution of Prime Numbers, Kyoto University Research Information Repository, October 1994. MR1370273 (97a:11141).

MAPLE

A305444 := proc(n) mul(d - 2, d = numtheory[factorset](n) minus {2}) end proc:

MATHEMATICA

a[n_] := If[n == 1, 1, Times @@ (DeleteCases[FactorInteger[n][[All, 1]], 2] - 2)];

Array[a, 100] (* Jean-Fran├žois Alcover, Apr 08 2020*)

PROG

(PARI) a(n)={my(f=factor(n>>valuation(n, 2))[, 1]); prod(i=1, #f, f[i]-2)} \\ Andrew Howroyd, Aug 12 2018

CROSSREFS

Cf. A173557.

Sequence in context: A339903 A187367 A307410 * A002945 A171232 A093423

Adjacent sequences:  A305441 A305442 A305443 * A305445 A305446 A305447

KEYWORD

nonn,easy,mult

AUTHOR

Markus Sigg, Aug 12 2018

STATUS

approved

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Last modified May 18 04:07 EDT 2021. Contains 343994 sequences. (Running on oeis4.)