

A054243


Number of partitions of n into distinct positive parts <= n, where parts are combined by XOR.


7



1, 1, 1, 2, 2, 4, 8, 16, 16, 32, 64, 128, 256, 512, 1024, 2048, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 67108864, 134217728, 268435456, 536870912
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OFFSET

0,4


COMMENTS

Usually successive powers of 2, but "stutters" when n is power of 2. (G.f. must satisfy some interesting functional equations!). Empty partition of 0 defined as 1.
This is an instance of what I like to call "numbral theory": whenever you have a set of indexed objects that you can do some kind of arithmetic on, then the indices act as "shadows" of the objects and you can generally talk about lots of analogs, such as partitions, primes, even generating functions, etc. It would be worthwhile to systematically "fill out" the entries for as many of these systems as possible in the OEIS.
The "AND" version is just the allones sequence.  Christian G. Bower, Jun 07 2005
a(n) is the number of orbits of the FlipAfter1 map on integers with n+1 binary digits. The FlipAfter1 map on an integer in binary form is: flip each bit that is immediately preceded by a "1". For example, the orbits on 4bit numbers are 1000 > 1100 > 1010 > 1111 and 1001 > 1101 > 1011 > 1110. The orbits on nbit numbers are all of length 2^floor(log_2(n1)+1) (for n >= 2), A062383. There is precisely one member of each orbit in the following set: integers in binary form such that each bit at distance a power of two from the leading "1" is 0. This set of orbit representatives begins 1, 10, 100, 1000, 1001, 10000, 10010, 100000, 100001, 100100, 100101.  David Callan, Oct 13 2012


LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000
Index to divisibility sequences


FORMULA

a(n) = 2^floor(n  log_2(n)  1) = A000079(n)/A062383(n).  Henry Bottomley, Nov 22 2001


EXAMPLE

a(5)=4 thus: 5 4+1 5+3+2+1 4+3+2 (where "+" = XOR).


MATHEMATICA

a[n_] := 2^(n  Ceiling[ Log[2, n] ]  1); Table[a[n], {n, 1, 36}] (* JeanFrançois Alcover, Apr 04 2013 *)


PROG

(PARI) a(n)=2^(n1log(n+.5)\log(2)) \\ Charles R Greathouse IV, Apr 08 2012


CROSSREFS

InclusiveOR (or IOR) version: A054244.
Cf. A160473.
Sequence in context: A222386 A222935 A279059 * A289670 A005864 A112433
Adjacent sequences: A054240 A054241 A054242 * A054244 A054245 A054246


KEYWORD

easy,nonn,nice


AUTHOR

Marc LeBrun, Feb 08 2000


STATUS

approved



