%I #13 Apr 25 2016 11:45:31
%S 1,1,3,63,16777215,1329227995784915872903807060280344575
%N a(1) = 1, for n >= 2: a(n) = (a(n-1)+1)^(n-1) - 1.
%C The next term (a(7)) has 217 digits.
%F a(n+1) = 2^A000142(n) - 1; A000142 = factorial numbers.
%e For n = 4: a(4) = (3+1)^3 - 1 = 63.
%o (PARI) a(n)=if(n<=1,1,(a(n-1)+1)^(n-1)-1); /* _Joerg Arndt_, Jun 10 2011 */
%K nonn,easy
%O 1,3
%A _Jaroslav Krizek_, Nov 03 2010