A337823 - OEIS

%I #17 Jun 13 2022 03:01:47

%S 1,2,2,4,5,9,9,13,13,17,21,21,27,28,29,33,37,41,41,47,48,49,55,56,61,

%T 67,68,69,73,73,77,89,87,94,92,103,100,107,110,112,117,121,121,131,

%U 128,133,133,145,151,152,153,157,161,161,171,172,177,181,181,187

%N a(n) = prime(n-1) - floor(a(n-1)/2); a(1)=1.

%e a(2) = prime(1) - floor(a(1)/2) =  2 - floor(1/2) = 2,

%e a(3) = prime(2) - floor(a(2)/2) =  3 - floor(2/2) = 2,

%e a(4) = prime(3) - floor(a(3)/2) =  5 - floor(2/2) = 4,

%e a(5) = prime(4) - floor(a(4)/2) =  7 - floor(4/2) = 5,

%e a(6) = prime(5) - floor(a(5)/2) = 11 - floor(5/2) = 9.

%t a[1] = 1; a[n_] := a[n] = Prime[n - 1] - Floor[a[n - 1]/2]; Array[a, 100] (* _Amiram Eldar_, Sep 24 2020 *)

%o (Ruby) require 'prime'

%o values = [1]

%o Prime.each(100) { |prime| values << prime - values[-1] / 2 }

%o p values

%o (PARI) a(n) = if (n<=2, n, prime(n-1) - floor(a(n-1)/2)); \\ _Michel Marcus_, Oct 07 2020; corrected Jun 13 2022

%Y Cf. A000040. Similar to A337724 that has step size 2, instead of 1 here.

%K nonn

%O 1,2

%A _Simon Strandgaard_, Sep 24 2020