A373803 Indices of primes in A373801.

1, 3, 6, 10, 19, 23, 25, 29, 31, 33, 36, 45, 48, 60, 91, 95, 101, 105, 108, 112, 116, 121, 124, 129, 142, 149, 155, 157, 161, 163, 173, 176, 185, 227, 229, 231, 238, 240, 386, 391, 393, 398, 411, 415, 435, 439, 466, 537, 543, 565, 570, 575, 577, 588, 592, 687, 694, 696, 700, 733, 738, 759

Offset: 1

Author

N. J. A. Sloane, Aug 05 2024

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..442 (first 91 terms from N. J. A. Sloane)

Crossrefs

Cf. A373801, A373802.

Programs

Maple

b:= proc(n) option remember; (m->
     `if`(isprime(m), ithprime(n)+1, 2*m-1))(b(n-1))
    end: b(1):=2:
a:= proc(n) option remember; local k; for k from 1+a(n-1)
      while not isprime(b(k)) do od; k
    end: a(0):=0:
seq(a(n), n=1..62);  # Alois P. Heinz, Aug 05 2024

Mathematica

Reap[Module[{n = 1}, Nest[If[n++; PrimeQ[#], Sow[n-1]; Prime[n] + 1, 2*# - 1] &, 2, 1000]]][[2,1]] (* Paolo Xausa, Aug 07 2024 *)

Python

from itertools import count
from sympy import isprime, nextprime
def A373803_gen(): # generator of terms
    a, p = 2, 3
    for i in count(1):
        if isprime(a):
            yield i
            a = p+1
        else:
            a = (a<<1)-1
        p = nextprime(p)
A373803_list = list(islice(A373803_gen(),20)) # Chai Wah Wu, Aug 05 2024