OFFSET
0,3
COMMENTS
Originally called "Exprimorial numbers (exponential prime factorials)", the strict analog would be "exponential primorial". [Editor's Note]
LINKS
FORMULA
a(n) = 0 if n = 0; a(n) = prime(n) ^ a(n - 1), n >= 1.
EXAMPLE
a(4) = 7 ^ a(3) = 7 ^ 125.
a(5) = 11 ^ a(4) has approximately 4.5 * 10^105 digits, starting with 335856... and ending in ...815171.
PROG
(C) unsigned long Exprimorial(unsigned int n) {
if (n == 0) return 0;
return pow(prime(n), Exprimorial(n - 1));
}
(PARI) vector(4, i, t=if(i==1, 1, prime(i)^t)) /* indices are shifted by 1 */ \\ M. F. Hasler, Nov 01 2009
CROSSREFS
KEYWORD
nonn
AUTHOR
ShaoJun Ying (dolphinysj(AT)gmail.com), Dec 14 2008
EXTENSIONS
Edited by M. F. Hasler, Nov 01 2009
STATUS
approved