A379477 Numbers k such that A003961(k)-2k and A003961(k)-sigma(k) have a common divisor > 1, where A003961 is fully multiplicative with a(prime(i)) = prime(i+1), and sigma is the sum of divisors function.

6, 7, 13, 18, 19, 24, 28, 30, 31, 37, 42, 43, 46, 54, 55, 60, 61, 66, 67, 68, 69, 72, 78, 79, 90, 91, 96, 97, 102, 103, 106, 109, 114, 120, 126, 127, 131, 132, 135, 138, 139, 140, 146, 150, 151, 162, 163, 166, 168, 174, 175, 180, 181, 186, 193, 198, 199, 200, 204, 210, 216, 222, 223, 229, 234, 240, 241, 246, 251

Offset: 1

Author

Antti Karttunen, Dec 23 2024

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000
• Index entries for sequences where odd perfect numbers must occur, if they exist at all
• Index entries for sequences related to prime indices in the factorization of n.
• Index entries for sequences related to sigma(n).

Crossrefs

Cf. A000203, A003961, A252748, A286385, A379476 (characteristic function).

Positions of terms > 1 in A326057.

Disjoint union of A372566 and A379479.

Subsequences: A000396. See also A378980.

Programs

PARI

is_A379477 = A379476;

Formula

{k such that gcd(A252748(k), A286385(k)) > 1}.