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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.
0
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
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 * A368628 A282036 A373817
KEYWORD
nonn
AUTHOR
Jon Perry, May 31 2003
EXTENSIONS
Edited by Don Reble, Nov 07 2005
STATUS
approved