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!)
A110590 Balanced numbers n (A020492) such that phi(n) is not divisible by 12. 1
1, 2, 3, 6, 12, 14, 15, 30, 264, 3828 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The only balanced numbers such that sigma(n) is not divisible by 12 are 1, 2, 3.

a(11) if it exists is greater than 10^8. - Michel Marcus, Aug 06 2013

a(11) if it exists is greater than 10^13. - Giovanni Resta, Jul 13 2015

LINKS

Table of n, a(n) for n=1..10.

FORMULA

n such that sigma(n)/phi(n) is an integer and phi(n) mod 12 != 0.

MAPLE

with(numtheory): BNM:=[]: for z from 1 to 1 do for n from 1 to 100000 do if phi(n) mod 12 > 0 and sigma(n) mod phi(n) = 0 then BNM:=[op(BNM), n] fi; od; od; BNM; # after 3828 there no others up to 2*10^6.

MATHEMATICA

fQ[n_] := Block[{ds = DivisorSigma[1, n], ep = EulerPhi@n}, Mod[ep, 12] > 0 && IntegerQ[ds/ep]]; Do[ If[ fQ@n, Print@n], {n, 4*10^8}] (* Robert G. Wilson v, Jun 19 2006 *)

CROSSREFS

Cf. A000010, A000203, A020492.

Sequence in context: A015765 A015771 A020492 * A329401 A291174 A281110

Adjacent sequences:  A110587 A110588 A110589 * A110591 A110592 A110593

KEYWORD

nonn,more

AUTHOR

Walter Kehowski, Sep 13 2005

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 February 20 22:47 EST 2020. Contains 332086 sequences. (Running on oeis4.)