OFFSET
1,1
FORMULA
a(n) = prime^{prime(n)}(n), with prime^{0}(n) = n and prime^{k}(n) = prime(prime^{k-1}(n)) for 1 <= k <= prime(n).
a(n) = prime(prime(...(n))) {prime(n) times}.
EXAMPLE
a(1) = prime(prime(1)) = 3.
a(2) = prime(prime(prime(2))) = 11.
a(3) = prime(prime(prime(prime(prime(3))))) = 709.
MATHEMATICA
nterms=6; Table[Nest[Prime[#]&, n, Prime[n]], {n, nterms}]
PROG
(Python)
from sympy import prime
def a(n):
iter = pn = prime(n)
for i in range(1, pn): iter = prime(iter)
return iter
print([a(n) for n in range(1, 6)]) # Michael S. Branicky, Jun 03 2021
(PARI) a(n) = my(p = n); for (k=1, prime(n), p=prime(p)); p; \\ Michel Marcus, Jun 03 2021
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Paolo Xausa, Jun 03 2021
EXTENSIONS
a(7) from Jinyuan Wang, Jul 12 2021
STATUS
approved