login
A280619
Integers m such that sigma(m) - eulerphi(m) <= 4*sqrt(m).
1
1, 2, 3, 4, 5, 7, 8, 9, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 131, 137, 139, 149, 151, 157, 163, 167, 169, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241
OFFSET
1,2
COMMENTS
Equals {1, 8} union A000430 (primes and square of primes).
Equals 8 union A166684.
LINKS
Mathematical Reflections, Solution to Problem O261, Issue 3, 2013, p. 24.
MATHEMATICA
Select[Range[250], DivisorSigma[1, #]-EulerPhi[#]<=4Sqrt[#]&] (* Harvey P. Dale, Jul 10 2018 *)
PROG
(PARI) isok(n) = sigma(n) - eulerphi(n) <= 4*sqrt(n); \\ Michel Marcus, Jan 06 2017
CROSSREFS
A000430 is the main entry for this sequence.
Sequence in context: A339841 A087797 A340815 * A282136 A371812 A153730
KEYWORD
nonn,easy
AUTHOR
Michel Marcus, Jan 06 2017
STATUS
approved