cp's OEIS Frontend

A046809 a(n) is the least integer greater than a(n-1) such that a(n-1)*2^a(n) - 1 is prime, a(1) = 1.

%I A046809 #24 Aug 11 2025 21:41:01
%S A046809 1,2,4,5,8,10,11,26,286,365,602,630,713,808,1327,3561,3566,5286,5477,
%T A046809 10600,13485,15441,17339,76856,277718,279098,977278,3437687,3564664,
%U A046809 3883403,4254462,4972164
%N A046809 a(n) is the least integer greater than a(n-1) such that a(n-1)*2^a(n) - 1 is prime, a(1) = 1.
%C A046809 Previous name was: Recursive sequence of indices of Proth primes a*2^b - 1.
%H A046809 Chris K. Caldwell, The Prime Pages, <a href="https://t5k.org/primes/page.php?id=138149">488639*2^3437688-1 (977278*2^3437687-1)</a>
%H A046809 Chris K. Caldwell, The Prime Pages, <a href="https://t5k.org/primes/page.php?id=138658">3437687*2^3564664-1</a>
%H A046809 Chris K. Caldwell, The Prime Pages, <a href="https://t5k.org/primes/page.php?id=140202">445583*2^3883406-1 (3564664*2^3883403-1)</a>
%H A046809 Chris K. Caldwell, The Prime Pages, <a href="https://t5k.org/primes/page.php?id=140608">3883403*2^4254462-1</a>
%H A046809 Chris K. Caldwell, The Prime Pages, <a href="https://t5k.org/primes/page.php?id=140860">2127231*2^4972165-1 (4254462*2^4972164-1)</a>
%H A046809 Y. Gallot, <a href="http://www.utm.edu/research/primes/programs/gallot/index.html">Proth.exe: Windows Program for Finding Large Primes</a>
%o A046809 (PARI) a=1;until(,print1(a,", ");for(b=a+1,+oo,if(ispseudoprime(a*2^b-1),a=b;break()))) \\ _Jeppe Stig Nielsen_, Apr 29 2022
%Y A046809 Cf. A046808.
%K A046809 hard,nonn,more
%O A046809 1,2
%A A046809 Chad Davis (cad16(AT)po.cwru.edu)
%E A046809 a(25)-a(27) from _Kellen Shenton_ Apr 29 2022
%E A046809 a(28)-a(32) from _Kellen Shenton_, Jun 15 2025