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A087087 Coprime sets of integers, each subset mapped onto a unique binary integer, values here shown in decimal. 1
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 28, 29, 32, 33, 48, 49, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 76, 77, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 92, 93, 96, 97, 112, 113, 128, 129, 132, 133, 144, 145, 148, 149, 192, 193, 196, 197 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

A coprime set of integers has no pair of elements for which (i,j)=0. Each element i in a subset contributes 2^(i-1) to the binary value for that subset. The integers missing from the sequence correspond to non-coprime subsets.

REFERENCES

Alan Sutcliffe, Divisors and Common Factors in Sets of Integers, awaiting publication.

LINKS

Ivan Neretin, Table of n, a(n) for n = 0..3232 (all terms up to 2^20)

EXAMPLE

a(11)=13 since the 11th coprime set counting from 0 is {4,3,1}, which maps onto 1101 binary = 13 decimal.

MATHEMATICA

a = {}; Do[set = Select[Range[Log2[n] + 1], Reverse[IntegerDigits[n, 2]][[#]] == 1 &]; If[Union@Flatten@Outer[If[#1 == #2, 1, GCD[#1, #2]] &, set, set] == {1}, AppendTo[a, n]], {n, 200}]; a (* Ivan Neretin, Aug 14 2015 *)

CROSSREFS

A087086 gives the corresponding values for the primitive sets of integers. A084422 gives the number of coprime subsets of the integers 1 to n.

Sequence in context: A178338 A048097 A130843 * A326675 A050742 A290387

Adjacent sequences:  A087084 A087085 A087086 * A087088 A087089 A087090

KEYWORD

easy,nonn,base

AUTHOR

Alan Sutcliffe (alansut(AT)ntlworld.com), Aug 16 2003

STATUS

approved

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Last modified August 19 21:19 EDT 2019. Contains 326133 sequences. (Running on oeis4.)