%I
%S 1,2,1,4,4,2,6,8,1,4,4,12,10,2,16,12,8,6,8,1,20,16,24,4,18,24,4,12,10,
%T 16,22,2,36,16,32,12,8,40,6,36,28,8,30,24,1,48,20,16,44,24,4,36,32,18,
%U 60,24,4,16,40,12,64,42,56,10,16,72,22,60,46,72,2
%N To obtain a(n), write the nth composite number as a product of primes, subtract 1 from each prime and multiply.
%H Alois P. Heinz, <a href="/A249140/b249140.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A003958(A002808(n)).  _Michel Marcus_, Oct 22 2014
%e a(1)=1 because the 1st composite number is 4, and the prime factors of 4 are (2,2): (21)*(21)=1.
%e a(4)=4 because the 4th composite number is 9, and the prime factors of 9 are (3,3): (31)*(31)=4.
%e a(19)=8 because the 19th composite number is 30, and the prime factors of 30 are (2,3,5): (21)*(31)*(51)=8.
%p b:= proc(n) option remember; local k;
%p for k from 1+`if`(n=1, 3, b(n1))
%p while isprime(k) do od; k
%p end:
%p a:= n> mul((i[1]1)^i[2], i=ifactors(b(n))[2]):
%p seq(a(n), n=1..100); # _Alois P. Heinz_, Oct 23 2014
%Y Cf. A002808, A003958, A114434.
%K nonn,easy
%O 1,2
%A _Gil Broussard_, Oct 22 2014
