login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A027761 Numerator of sum_{p prime, p-1 divides 2*n} 1/p. 3
5, 31, 41, 31, 61, 3421, 5, 557, 821, 371, 121, 3421, 5, 929, 15745, 557, 5, 2557843, 5, 15541, 1805, 743, 241, 60887, 61, 1673, 821, 929, 301, 79085411, 5, 557, 66961, 31, 4397, 188641729, 5, 31, 3281, 277727, 421, 4462547, 5, 66817, 313477, 1487, 5, 5952449 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..10000

MATHEMATICA

a[n_] := Sum[ Boole[ PrimeQ[d+1] ]/(d+1), {d, Divisors[2n]}] // Numerator; Table[a[n], {n, 1, 48}] (* Jean-François Alcover, Aug 10 2012 *)

PROG

(PARI)

a(n)=

{

my(bd=0);

forprime (p=2, 2*n+1, if( (2*n)%(p-1)==0, bd += 1/p; ) );

bd = numerator(bd);

return(bd);

}

/* Joerg Arndt, May 06 2012 */

CROSSREFS

Cf. A027762.

Sequence in context: A042837 A354881 A162173 * A166306 A341632 A287300

Adjacent sequences: A027758 A027759 A027760 * A027762 A027763 A027764

KEYWORD

nonn,frac

AUTHOR

N. J. A. Sloane.

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 29 11:47 EST 2023. Contains 359922 sequences. (Running on oeis4.)