A339968 Numbers k such that sigma(k) and k+2 are relatively prime, where sigma gives the sum of divisors of k.

1, 2, 3, 4, 5, 7, 9, 11, 13, 15, 16, 17, 18, 19, 21, 23, 25, 27, 29, 31, 32, 33, 35, 36, 37, 39, 41, 43, 45, 47, 50, 51, 53, 57, 59, 61, 64, 65, 67, 69, 71, 72, 73, 75, 77, 79, 81, 83, 87, 89, 91, 93, 95, 97, 98, 99, 100, 101, 103, 105, 107, 109, 111, 113, 119, 121, 123, 125, 127, 129, 131, 135, 137, 139, 141, 143

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..25064

Index entries for sequences where odd perfect numbers must occur, if they exist at all

Index entries for sequences related to sigma(n)

Prog

(PARI) isA339968(n) = (1==gcd(sigma(n), n+2));

Crossrefs

Positions of ones in A339967.

Cf. A000203

Cf. also A014567, A339963.

Sequence in context: A064005 A306587 A353301 * A316268 A026285 A013930

Adjacent sequences: A339965 A339966 A339967 * A339969 A339970 A339971

Keyword

nonn

Author

Antti Karttunen, Dec 25 2020

Status

approved