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A372730
Number of primes <= A005867(n).
1
0, 0, 1, 4, 15, 92, 757, 8899, 125261, 2232782, 51902553, 1327191561, 41351244491, 1452937916515, 54332144724834, 2246960940148460, 105818707666943651, 5595105626396158784, 308241771351984486729, 18772520681296116861073
OFFSET
0,4
FORMULA
a(n) = A000720(A005867(n)).
EXAMPLE
a(3) = 4 because there are 4 primes less than A005867(3) = 8: 2, 3, 5 and 7.
PROG
(Python)
from sympy import prime, primepi
p = 1
l = [0]
for i in range(1, 12):
p *= (prime(i) - 1)
l.append(primepi(p))
print(l)
(PARI) A372730(n) = primepi(prod(k=1, n, prime(k)-1)); \\ Antti Karttunen, May 22 2024
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Alexandre Herrera, May 11 2024
EXTENSIONS
a(9)-a(11) from Antti Karttunen, May 22 2024
a(12)-a(16) from Amiram Eldar, May 22 2024
a(17)-a(18) from Chai Wah Wu, Jun 04 2024
a(19) from Chai Wah Wu, Jun 05 2024
STATUS
approved