login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A097702 a(n) = (A063880(n) - 108)/216. 3
0, 2, 3, 5, 6, 8, 9, 11, 14, 15, 17, 18, 20, 21, 23, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44, 45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 63, 65, 66, 68, 69, 71, 72, 74, 75, 77, 78, 80, 81, 83, 86, 89, 90, 92, 93, 95, 96, 98, 99, 101, 102, 104, 105, 107, 108, 110 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Conjecture: n is a member iff 6*n+3 is squarefree. - Vladeta Jovovic, Aug 27 2004

It is only a conjecture that all terms are integers (confirmed up to 10^6 by Robert G. Wilson v).

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

MATHEMATICA

usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; (Select[ Range[ 24500], DivisorSigma[1, # ] == 2usigma[ # ] &] - 108)/216 (* Robert G. Wilson v, Aug 28 2004 *)

PROG

(PARI) {u(n)=sumdiv(n, d, if(gcd(d, n/d)==1, d))} n=2:while(1, n++: if(sigma(n)==2*u(n), print1((n-108)/216", ")))

CROSSREFS

Cf. A097703.

Sequence in context: A094820 A309793 A093689 * A082583 A274332 A005097

Adjacent sequences:  A097699 A097700 A097701 * A097703 A097704 A097705

KEYWORD

nonn

AUTHOR

Ralf Stephan, Aug 26 2004

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 July 28 19:33 EDT 2021. Contains 346335 sequences. (Running on oeis4.)