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A046687
Numbers k such that k and sum of 4th powers of divisors of k are relatively prime.
5
1, 2, 3, 4, 5, 7, 8, 9, 11, 13, 15, 16, 17, 18, 19, 21, 23, 25, 27, 29, 31, 32, 33, 35, 37, 39, 41, 43, 45, 47, 49, 50, 51, 53, 55, 57, 59, 61, 64, 65, 67, 69, 71, 72, 73, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 98, 99, 100, 101, 103, 105, 107, 109, 111, 113, 115, 119
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
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