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A230203 Numbers n such that sigma(phi(n)) > n. 4
5, 7, 9, 11, 13, 17, 19, 21, 23, 25, 26, 27, 29, 31, 33, 35, 37, 38, 39, 41, 43, 45, 47, 49, 51, 52, 53, 55, 56, 57, 59, 61, 62, 63, 65, 67, 69, 71, 73, 74, 75, 76, 77, 79, 81, 82, 83, 85, 86, 87, 88, 89, 91, 93, 95, 97, 99, 101, 103, 104, 105, 107, 109, 111, 112, 113, 115, 116, 117, 119 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
It seems that the odd number n isn't in the sequence if and only if n+2 is Fermat prime.
LINKS
MAPLE
for n do if sigma(phi(n))>n then print{n} fi od:
MATHEMATICA
Select[Range[150], DivisorSigma[1, EulerPhi[#]]>#&] (* Harvey P. Dale, Apr 14 2019 *)
CROSSREFS
Sequence in context: A005763 A035034 A065155 * A339910 A303578 A282057
KEYWORD
nonn
AUTHOR
Vladimir Letsko, Oct 11 2013
STATUS
approved

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Last modified February 25 19:44 EST 2024. Contains 370332 sequences. (Running on oeis4.)