login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A175020 An integer n is included if n is the smallest positive integer with its particular multiset of run-lengths (of either 0 or 1 considered together) in its binary representation. 6
1, 2, 3, 4, 5, 7, 8, 9, 10, 12, 15, 16, 17, 18, 19, 21, 24, 31, 32, 33, 34, 35, 36, 37, 42, 48, 51, 56, 63, 64, 65, 66, 67, 68, 69, 71, 73, 74, 76, 85, 96, 99, 112, 127, 128, 129, 130, 131, 132, 133, 135, 136, 137, 138, 140, 146, 147, 149, 170, 192, 195, 199, 204, 224 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

This sequence gives a way to enumerate unrestricted partitions of a number. The number of terms of this sequence that are each >= 2^(k-1) and <= 2^k -1 is equal to the number of unrestricted partitions of k.

Equivalently, numbers in whose binary representation the runs of 1's are in increasing order of length, the runs of 0's are in decreasing order of length, and all runs of 0's are at least as long as any run of 1's. The position of [1^m] in the partitions of m will be P(m-1). It is the last partition in the list with a part of size 1; anything with a part of size 2 or more will start 100... in the binary representation, while this partition starts 101...; and any partition that does not have a part of size 1 will start 11.... Removing one part of size 1 from the partitions of size m that have such a part gives each partition of m-1 uniquely. This relationship is expressed by the second formula of A002865. - Franklin T. Adams-Watters, Nov 03 2009

A000975 is a subsequence. - Alford Arnold, Nov 09 2009

LINKS

Table of n, a(n) for n=1..64.

EXAMPLE

9 in binary is 1001. The run lengths form the multiset (1,2,1). Since no positive integer < 9 has this same multiset of run lengths, then 9 is in this sequence. On the other hand, 23 in binary is 10111. The run-lengths are (1,1,3). But 17 (which is < 23) in binary is 10001, which has the run-lengths of (1,3,1). Since the multisets (1,1,3) and (1,3,1) are identical, then 23 is not in this sequence.

MAPLE

runLSet := proc(n) option remember ; local bdg, lset, arl, p ; bdg := convert(n, base, 2) ; lset := [] ; arl := -1 ; for p from 1 to nops(bdg) do if p = 1 then arl := 1 ; elif op(p, bdg) = op(p-1, bdg) then arl := arl+1 ; else if arl > 0 then lset := [arl, op(lset)] ; end if; arl := 1 ; end if; end do ; if arl > 0 then lset := [arl, op(lset)] ; end if; return lset ; end proc:

isA175020 := proc(n) local thisLset, k ; thisLset := runLSet(n) ; for k from 1 to n-1 do if convert(runLSet(k), multiset) = convert(thisLset, multiset) then return false; end if; end do ; return true; end proc:

for n from 1 to 300 do if isA175020(n) then printf("%d, ", n) ; end if; end do;

# R. J. Mathar, Feb 27 2010

CROSSREFS

Complement is A175021.

Cf. A175021, A175022, A175023, A175024, A000975.

Sequence in context: A024898 A094210 A165256 * A050728 A230999 A180590

Adjacent sequences:  A175017 A175018 A175019 * A175021 A175022 A175023

KEYWORD

base,nonn

AUTHOR

Leroy Quet, Nov 03 2009

EXTENSIONS

More terms from Alford Arnold, Nov 09 2009

Terms beyond 64 by R. J. Mathar, Feb 27 2010

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified March 23 21:31 EDT 2017. Contains 283985 sequences.