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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
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
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
KEYWORD
easy,nonn
AUTHOR
Ryan Propper, Jul 11 2005
EXTENSIONS
Extended by Ray Chandler, Jul 24 2005
STATUS
approved

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Last modified March 3 00:22 EST 2024. Contains 370499 sequences. (Running on oeis4.)