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%I #13 Jun 25 2022 21:54:36
%S 1,3,4,15,6,91,8,127,40,217,12,5080,14,399,403,2047,18,16395,20,19812,
%T 741,931,24,991111,156,1281,1093,50800,30,2929531,32,65535,1729,2149,
%U 1767,30203052,38,2667,2379,6397171,42,10506551,44,185928,170508,3871,48
%N a(n) = sum of the divisors of the product of the divisors of n.
%F a(n) = A000203(A007955(n)).
%F a(p) = p + 1 for p = primes (A000040).
%F a(A000079(n)) = 2* A007955(n)) - 1.
%e For n = 4; a(n) = sigma (1*2*4) = sigma(8) = 15.
%o (Magma) [&+[d: d in Divisors(&*[d: d in Divisors(n)])]: n in [1..100]]
%o (Python)
%o from math import isqrt
%o from sympy import divisor_sigma
%o 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
%Y Cf. A000079, A000040, A000203, A007955, A280582, A280684.
%K nonn
%O 1,2
%A _Jaroslav Krizek_, Jan 07 2017
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