%I #19 Nov 26 2018 17:01:47
%S 1,2,18,68664550781250
%N a(1) = 1; thereafter a(n) = a(n1) * prime(n1)^a(n1).
%C The prime factorization of a(n) describes all previous terms in the sequence: a(n) = prime(1)^a(1) * prime(2)^a(2) * prime(3)^a(3) * ...* prime(n1)^a(n1).
%C An infinite and monotonically increasing sequence which grows very rapidly.
%e 68664550781250 = 2 * 3^2 * 5^18 = prime(1)^1 * prime(2)^2 * prime(3)^18.
%t Nest[Append[#, #[[1]] Prime[Length@ #]^#[[1]] ] &, {1}, 3] (* _Michael De Vlieger_, Nov 05 2018 *)
%o (PARI) apply( ppp(n) = prod(i=1, n1, prime(i)^ppp(i)), [1..4] )
%Y Somewhat similar to A007097.
%Y Cf. A321339.
%K nonn
%O 1,2
%A _Russell Y. Webb_, Nov 05 2018
