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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.

%I A108853 #10 Feb 16 2025 08:32:58
%S A108853 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 A108853 70,71,72,73,74,75,76,77,78,121,122,123,124,125,126,136,137,138,159,
%U A108853 160,161,162,190,191,192,202,203,204,205,206,207,208,209,210,211,212,213
%N A108853 Indices of prime Knuth numbers; that is, integers n such that the n-th Knuth number is prime. Indices of primes in A007448.
%H A108853 Michael S. Branicky, <a href="/A108853/b108853.txt">Table of n, a(n) for n = 1..10000</a>
%H A108853 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/KnuthNumber.html">Knuth Number.</a>
%e A108853 10 is a term because the 10th Knuth number, 13, is prime.
%o A108853 (Python)
%o A108853 from sympy import isprime, primepi
%o A108853 from itertools import count, islice
%o A108853 def agen():
%o A108853     A007448n, A007448lst = 1, [1]
%o A108853     for n in count(0):
%o A108853         if isprime(A007448n):
%o A108853             yield n
%o A108853         A007448n = 1 + min(2*A007448lst[n//2], 3*A007448lst[n//3])
%o A108853         A007448lst.append(A007448n)
%o A108853 print(list(islice(agen(), 61))) # _Michael S. Branicky_, Jul 15 2022
%Y A108853 Cf. A007448.
%K A108853 easy,nonn
%O A108853 1,2
%A A108853 _Ryan Propper_, Jul 11 2005
%E A108853 Extended by _Ray Chandler_, Jul 24 2005