OFFSET
1,2
COMMENTS
All even terms are either squares or doubled squares. - Ivan Neretin, Dec 30 2015
The asymptotic density of this sequence is 0 (Dressler, 1974). - Amiram Eldar, Jul 23 2020
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10076
Robert E. Dressler, On a theorem of Niven, Canadian Mathematical Bulletin, Vol. 17, No. 1 (1974), pp. 109-110.
MATHEMATICA
Select[Range[120], GCD[#, DivisorSigma[4, #]] == 1 &] (* Ivan Neretin, Dec 30 2015 *)
Select[Range[150], CoprimeQ[#, DivisorSigma[4, #]]&] (* Harvey P. Dale, Jan 15 2024 *)
PROG
(PARI) isok(n) = gcd(n, sigma(n, 4)) == 1; \\ Michel Marcus, Dec 20 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved