A068402 - OEIS

A068402

Numbers n such that sigma(n+1)=n+phi(n).

4, 6, 32, 38, 54, 56, 84, 278, 2664, 10944, 15608, 20720, 84800, 179576, 209664, 6251904, 85505600, 125226624, 584003328, 19018936320, 20534891040, 79185129984, 87065548800, 191904215040, 964494300024

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OFFSET

1,1

COMMENTS

Are there any odd values in the sequence?

a(26) > 10^12. - Donovan Johnson, Feb 29 2012

LINKS

Table of n, a(n) for n=1..25.

MATHEMATICA

Select[Range[10^5], DivisorSigma[1, # + 1] == # + EulerPhi[#] &] (* Alonso del Arte, Feb 29 2012 *)

PROG

(PARI) : for(n=1, 500000, if(sigma(n+1)-n==eulerphi(n), print1(n, ", ")))

CROSSREFS

Sequence in context: A088255 A192083 A068720 * A078250 A239224 A087299

Adjacent sequences: A068399 A068400 A068401 * A068403 A068404 A068405

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Mar 02 2002

EXTENSIONS

One more term from Rick L. Shepherd, Jun 21 2002

a(17)-a(25) from Donovan Johnson, Feb 29 2012

STATUS

approved