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Indices of prime Knuth numbers; that is, integers n such that the n-th Knuth number is prime. Indices of primes in A007448.
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%I #9 Jul 15 2022 11:29:01

%S 1,2,4,5,6,10,11,12,15,16,17,18,28,29,30,40,41,42,64,65,66,67,68,69,

%T 70,71,72,73,74,75,76,77,78,121,122,123,124,125,126,136,137,138,159,

%U 160,161,162,190,191,192,202,203,204,205,206,207,208,209,210,211,212,213

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

%H Michael S. Branicky, <a href="/A108853/b108853.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/KnuthNumber.html">Knuth Number.</a>

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

%o (Python)

%o from sympy import isprime, primepi

%o from itertools import count, islice

%o def agen():

%o A007448n, A007448lst = 1, [1]

%o for n in count(0):

%o if isprime(A007448n):

%o yield n

%o A007448n = 1 + min(2*A007448lst[n//2], 3*A007448lst[n//3])

%o A007448lst.append(A007448n)

%o print(list(islice(agen(), 61))) # _Michael S. Branicky_, Jul 15 2022

%Y Cf. A007448.

%K easy,nonn

%O 1,2

%A _Ryan Propper_, Jul 11 2005

%E Extended by _Ray Chandler_, Jul 24 2005