A343226 - OEIS

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A343226

a(n) = gcd(sigma(n), n+A003415(n)), where A003415 is the arithmetic derivative, and sigma is the sum of divisors of n.

1, 3, 4, 1, 6, 1, 8, 5, 1, 1, 12, 28, 14, 1, 1, 1, 18, 39, 20, 2, 1, 1, 24, 4, 1, 1, 2, 4, 30, 1, 32, 7, 1, 1, 1, 1, 38, 1, 1, 18, 42, 1, 44, 4, 6, 1, 48, 4, 3, 1, 1, 2, 54, 15, 1, 4, 1, 1, 60, 8, 62, 1, 2, 1, 1, 1, 68, 14, 1, 3, 72, 3, 74, 1, 2, 4, 1, 1, 80, 2, 1, 1, 84, 16, 1, 1, 1, 12, 90, 3, 1, 4, 1, 1, 1, 4

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

a(n) = n+1 iff n is prime (A000040). - Bernard Schott, Jun 01 2021

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..20000

Index entries for sequences related to sigma(n)

FORMULA

a(n) = gcd(A000203(n), A129283(n)) = gcd(A000203(n), A211991(n)).

a(n) = A000203(n) / A343227(n).

a(n) = 1 if n is squarefree semiprime (A006881). - Bernard Schott, Jun 02 2021