A108853 Indices of prime Knuth numbers; that is, integers n such that the n-th Knuth number is prime. Indices of primes in A007448.

1, 2, 4, 5, 6, 10, 11, 12, 15, 16, 17, 18, 28, 29, 30, 40, 41, 42, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 121, 122, 123, 124, 125, 126, 136, 137, 138, 159, 160, 161, 162, 190, 191, 192, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213

Offset

1,2

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Knuth Number.

Example

10 is a term because the 10th Knuth number, 13, is prime.

Prog

(Python)
from sympy import isprime, primepi
from itertools import count, islice
def agen():
    A007448n, A007448lst = 1, [1]
    for n in count(0):
        if isprime(A007448n):
            yield n
        A007448n = 1 + min(2*A007448lst[n//2], 3*A007448lst[n//3])
        A007448lst.append(A007448n)
print(list(islice(agen(), 61))) # Michael S. Branicky, Jul 15 2022

Crossrefs

Cf. A007448.

Sequence in context: A140779 A348937 A117890 * A257085 A334736 A265349

Adjacent sequences: A108850 A108851 A108852 * A108854 A108855 A108856

Keyword

easy,nonn

Author

Ryan Propper, Jul 11 2005

Extensions

Extended by Ray Chandler, Jul 24 2005

Status

approved