A146768 a(n) is the number k such that 2^(2k+1)-1 = A000668(n+1).

1, 2, 3, 6, 8, 9, 15, 30, 44, 53, 63, 260, 303, 639, 1101, 1140, 1608, 2126, 2211, 4844, 4970, 5606, 9968, 10850, 11604, 22248, 43121, 55251, 66024, 108045, 378419, 429716, 628893, 699134, 1488110, 1510688, 3486296, 6733458, 10498005, 12018291, 12982475, 15201228

Offset: 1

Author

Artur Jasinski, Nov 02 2008

Keywords

• nonn

Comments

The least common multiple of an even superperfect number greater than 2 and its arithmetic derivative divided by the number itself, i.e., lcm(A061652(i), A061652(i)')/A061652(i). - Giorgio Balzarotti, Apr 21 2011

Links

• Amiram Eldar, Table of n, a(n) for n = 1..46
• C. K. Caldwell, Top 20 Mersenne primes
• Bernhard Helmes, Prime generator f(n)=2n^2-1
• George Woltman, Great Internet Mersenne Prime Search

Crossrefs

Cf. A000043, A000668, A061652.

Programs

Mathematica

(MersennePrimeExponent[Range[2, 47]] - 1)/2 (* Amiram Eldar, Mar 29 2020 *)

Formula

a(n) = (A000043(n+1) - 1)/2.

2^(2*a(n) + 1) - 1 = A000668(n+1). - M. F. Hasler, Jan 27 2020

Extensions

Term for the 39th Mersenne prime added by Roderick MacPhee, Oct 05 2009

Formula and edits from Charles R Greathouse IV, Aug 14 2010

Updated to include 40th Mersenne prime by Michael B. Porter, Nov 26 2010

a(40)-a(42) from Amiram Eldar, Mar 29 2020