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A067625
Numbers n such that sigma(n) = phi(prime(n)+1).
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
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
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 23 2002
EXTENSIONS
More terms from Klaus Brockhaus, Mar 02 2002
STATUS
approved