A165420 a(1) = 1, a(2) = 2, a(n) = product of the previous terms for n >= 3.

1, 2, 2, 4, 16, 256, 65536, 4294967296, 18446744073709551616, 340282366920938463463374607431768211456, 115792089237316195423570985008687907853269984665640564039457584007913129639936

Offset: 1

Author

Jaroslav Krizek, Sep 17 2009

Keywords

• nonn

Comments

Same as A001146 with 1 and 2 added in front. - Stanislav Sykora, Oct 05 2014

Links

• G. C. Greubel, Table of n, a(n) for n = 1..14

Crossrefs

Cf. A000079, A001146.

Programs

Mathematica

a[1]:= 1; a[2]:= 2; a[n_]:= Product[a[j], {j,1,n-1}]; Table[a[n], {n, 1, 12}] (* G. C. Greubel, Oct 19 2018 *)

PARI

{a(n) = if(n==1, 1, if(n==2, 2, prod(j=1, n-1, a(j))))};
for(n=1, 10, print1(a(n), ", ")) \\ G. C. Greubel, Oct 19 2018

Formula

a(1) = 1, a(2) = 2, a(n) = Product_{i=1..n-1} a(i), n >= 3.

a(1) = 1, a(2) = 2, a(n) = A000079(2^(n-3)) = A001146(n-3) = 2^(2^(n-3)), n >= 3.

a(1) = 1, a(2) = 2, a(3) = 2, a(n) = (a(n-1))^2, n >= 4.