

A065497


Number of (binary) bit strings of length n having at least one even length block of 0's followed by an even length block of 1's.


3



0, 0, 0, 0, 1, 2, 7, 16, 40, 92, 209, 468, 1027, 2242, 4832, 10360, 22049, 46694, 98419, 206588, 432132, 900980, 1873297, 3884904, 8038295, 16597478, 34205700, 70372728, 144550977, 296486538, 607301551, 1242406568, 2538762208, 5182207180
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

0,6


LINKS

Table of n, a(n) for n=0..33.
Index entries for linear recurrences with constant coefficients, signature (2,3,4,5,2).


FORMULA

G.f.: x^4/((1  2*x)*(1  3*x^2  2*x^3 + x^4)). [Corrected by Georg Fischer, May 15 2019]


EXAMPLE

a(6)=7 because of 000011, 001100, 001101, 001111, 010011, 100110, 110011.


MATHEMATICA

CoefficientList[Series[x^4/((1  2 x) (1  3 x^2  2 x^3 + x^4)), {x, 0, 33}], x] (* Georg Fischer, May 15 2019 *)


CROSSREFS

Cf. A065455, A065494, A065495.
Sequence in context: A041887 A129441 A093971 * A131727 A320236 A073371
Adjacent sequences: A065494 A065495 A065496 * A065498 A065499 A065500


KEYWORD

nonn,easy


AUTHOR

Len Smiley, Nov 24 2001


EXTENSIONS

Offset changed from 4 to 0 by Georg Fischer, May 15 2019


STATUS

approved



