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

%I A146768 #72 Apr 04 2025 14:35:15
%S A146768 1,2,3,6,8,9,15,30,44,53,63,260,303,639,1101,1140,1608,2126,2211,4844,
%T A146768 4970,5606,9968,10850,11604,22248,43121,55251,66024,108045,378419,
%U A146768 429716,628893,699134,1488110,1510688,3486296,6733458,10498005,12018291,12982475,15201228
%N A146768 a(n) is the number k such that 2^(2k+1)-1 = A000668(n+1).
%C A146768 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
%H A146768 Amiram Eldar, <a href="/A146768/b146768.txt">Table of n, a(n) for n = 1..46</a>
%H A146768 C. K. Caldwell, <a href="https://t5k.org/top20/page.php?id=4">Top 20 Mersenne primes</a>
%H A146768 Bernhard Helmes, <a href="http://devalco.de/quadr_Sieb_2x%5E2-1.php">Prime generator f(n)=2n^2-1</a>
%H A146768 George Woltman, <a href="http://www.mersenne.org/default.php">Great Internet Mersenne Prime Search</a>
%F A146768 a(n) = (A000043(n+1) - 1)/2.
%F A146768 2^(2*a(n) + 1) - 1 = A000668(n+1). - _M. F. Hasler_, Jan 27 2020
%t A146768 (MersennePrimeExponent[Range[2, 47]] - 1)/2 (* _Amiram Eldar_, Mar 29 2020 *)
%Y A146768 Cf. A000043, A000668, A061652.
%K A146768 nonn
%O A146768 1,2
%A A146768 _Artur Jasinski_, Nov 02 2008
%E A146768 Term for the 39th Mersenne prime added by _Roderick MacPhee_, Oct 05 2009
%E A146768 Formula and edits from _Charles R Greathouse IV_, Aug 14 2010
%E A146768 Updated to include 40th Mersenne prime by _Michael B. Porter_, Nov 26 2010
%E A146768 a(40)-a(42) from _Amiram Eldar_, Mar 29 2020