%I #15 Aug 01 2019 03:47:34

%S 1,4,12,12,10,36,14,8,9,60,22,12,26,112,15,32,17,36,38,40,21,44,23,

%T 216,50,26,216,56,58,90,62,64,33,68,35,72,74,38,312,40,82,504,86,132,

%U 45,46,94,96,49,100,612,104,159,108,55,112,570,58,118,720,61,124,63,512,390,66,134,68,138,70,852,144,219,74,150,608,77,156,948

%N a(n) = n*gcd(c(n), d(n)), where c(n) = composite numbers, d(n) = number of divisors of c(n).

%C Occurrences of primes: 3 (17, 23, 61) in first 80 terms.

%e For n = 4: 4th composite number is 9. 9 has 3 divisors (1,3,9), thus gcd(9,3) * 4 = 12.

%t Composites := Select[Range[2, 110], ! PrimeQ[#] &]; Composite[n_] := Last[Take[Composites, n]]; Table[GCD[Composite[n], DivisorSigma[0, Composite[n]]] n, {n, Length[Composites]}]

%Y Cf. A002808, A000005.

%K nonn,easy

%O 1,2

%A _Carlos Eduardo Olivieri_, Dec 27 2014