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A349165
Numbers k such that sigma(k) and A003961(k) are relatively prime, where A003961(n) is fully multiplicative function with a(prime(k)) = prime(k+1).
7
1, 3, 4, 5, 7, 9, 11, 12, 13, 15, 16, 17, 19, 21, 23, 25, 28, 29, 31, 33, 35, 36, 37, 39, 41, 43, 45, 47, 48, 49, 51, 52, 53, 55, 59, 61, 63, 64, 67, 69, 71, 73, 75, 76, 77, 79, 81, 83, 84, 85, 89, 91, 93, 95, 97, 101, 103, 105, 107, 109, 111, 112, 113, 115, 117, 119, 121, 123, 124, 125, 127, 129, 131, 133, 137, 139
OFFSET
1,2
PROG
(PARI)
A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };
isA349165(n) = (1==gcd(sigma(n), A003961(n)));
CROSSREFS
Positions of ones in A342671, and also in A349163.
Cf. A349166 (complement), A349167 (characteristic function).
Sequence in context: A361924 A187691 A141259 * A047501 A256455 A035242
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 09 2021
STATUS
approved