A067625 Numbers n such that sigma(n) = phi(prime(n)+1).

23, 51, 77, 87, 114, 154, 158, 184, 210, 308, 552, 690, 786, 1330, 1848, 2030, 2280, 2868, 2976, 3432, 8680, 10290, 11556, 12750, 13110, 26400, 56808, 57960, 62496, 136290, 170478, 608580

Offset

1,1

Comments

The sequence may be finite. Typically phi(prime(n)+1) will be on the order of n*log(n), while according to Grönwall's theorem sigma(n) = O(n * log log(n)). - Robert Israel, Sep 12 2014

Links

Table of n, a(n) for n=1..32.

Maple

with(numtheory): A067625:=n->`if`(sigma(n)=phi(ithprime(n)+1), n, NULL): seq(A067625(n), n=1..10^5); # Wesley Ivan Hurt, Sep 12 2014

Mathematica

Select[Range[610000], DivisorSigma[1, #]==EulerPhi[Prime[#]+1]&] (* Harvey P. Dale, Mar 17 2012 *)

Prog

(PARI) a067625(m) = for(n=1, m, if(sigma(n)==eulerphi(prime(n)+1), print1(n, ", ")))

Crossrefs

Sequence in context: A157095 A281266 A165432 * A140689 A172034 A335655

Adjacent sequences: A067622 A067623 A067624 * A067626 A067627 A067628

Keyword

nonn

Author

Benoit Cloitre, Feb 23 2002

Extensions

More terms from Klaus Brockhaus, Mar 02 2002

Status

approved