A083015 a(n) = the number of ordered pairs of n-bit bit strings, such that both bit strings have at least n/2 one-bits, or both have at most n/2 one-bits.

1, 2, 14, 32, 206, 512, 3128, 8192, 48238, 131072, 750584, 2097152, 11746424, 33554432, 184558304, 536870912, 2908113518, 8589934592, 45923227448, 137438953472, 726419131576, 2199023255552, 11506072128224, 35184372088832

Offset

0,2

Links

Table of n, a(n) for n=0..23.

Formula

a(n) = 4^n/2 + 2^n*c - c^2/2; where c is (n choose n/2) for even n, 0 for odd n.

Example

a(2)=14 because of the 16 ordered pairs, only (00,11) and (11,00) do not qualify.

Crossrefs

Sequence in context: A231050 A337338 A322074 * A378259 A368628 A282036

Adjacent sequences: A083012 A083013 A083014 * A083016 A083017 A083018

Keyword

nonn

Author

Jon Perry, May 31 2003

Extensions

Edited by Don Reble, Nov 07 2005

Status

approved