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 A280685 a(n) = sum of the divisors of the product of the divisors of n. 2
 1, 3, 4, 15, 6, 91, 8, 127, 40, 217, 12, 5080, 14, 399, 403, 2047, 18, 16395, 20, 19812, 741, 931, 24, 991111, 156, 1281, 1093, 50800, 30, 2929531, 32, 65535, 1729, 2149, 1767, 30203052, 38, 2667, 2379, 6397171, 42, 10506551, 44, 185928, 170508, 3871, 48 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA a(n) = A000203(A007955(n)). a(p) = p + 1 for p = primes (A000040). a(A000079(n)) = 2* A007955(n)) - 1. EXAMPLE For n = 4; a(n) = sigma (1*2*4) = sigma(8) = 15. PROG (Magma) [&+[d: d in Divisors(&*[d: d in Divisors(n)])]: n in [1..100]] (Python) from math import isqrt from sympy import divisor_sigma def A280685(n): return divisor_sigma((isqrt(n) if (c:=divisor_count(n)) & 1 else 1)*n**(c//2)) # Chai Wah Wu, Jun 25 2022 CROSSREFS Cf. A000079, A000040, A000203, A007955, A280582, A280684. Sequence in context: A194924 A205489 A343935 * A076365 A070971 A338438 Adjacent sequences: A280682 A280683 A280684 * A280686 A280687 A280688 KEYWORD nonn AUTHOR Jaroslav Krizek, Jan 07 2017 STATUS approved

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Last modified January 27 03:13 EST 2023. Contains 359836 sequences. (Running on oeis4.)