A175985 a(1) = 1, for n >= 2: a(n) = (a(n-1)+1)^(n-1) - 1.

1, 1, 3, 63, 16777215, 1329227995784915872903807060280344575

Offset: 1

Author

Jaroslav Krizek, Nov 03 2010

Keywords

• nonn
• easy

Comments

The next term (a(7)) has 217 digits.

Examples

			For n = 4: a(4) = (3+1)^3 - 1 = 63.
		

Programs

PARI

a(n)=if(n<=1,1,(a(n-1)+1)^(n-1)-1); /* Joerg Arndt, Jun 10 2011 */

Formula

a(n+1) = 2^A000142(n) - 1; A000142 = factorial numbers.