A080998 a(n) is n's rank among the positive integers in terms of centrality -the fraction of n represented by the average gcd of n and the positive integers, or A018804(n)/n^2 (cf. A080997).

1, 2, 3, 4, 6, 5, 10, 7, 11, 9, 18, 8, 20, 13, 12, 15, 25, 14, 33, 16, 21, 23, 40, 17, 32, 28, 27, 22, 53, 19, 56, 30, 35, 39, 36, 24, 69, 46, 43, 26, 79, 29, 89, 38, 37, 55, 95, 31, 67, 45, 57, 47, 108, 41, 60, 42, 65, 75

Offset

1,2

Links

Table of n, a(n) for n=1..58.

Example

a(5)=6 because the centrality of 5 is 9/25 (.36), which places it sixth among positive integers in centrality; it ranks behind 1 (whose centrality is 1), 2 (3/4, .75), 3 (5/9, .555...), 4 (1/2, .5) and 6 (5/12, .41666...).

Crossrefs

A080997 gives fuller description of centrality, as well as finite portion of the arrangement of positive integers in order of their centrality. For more about where numbers occur in A080997, see also A081000, A081001, A081028, A081029.

Sequence in context: A374798 A191545 A064275 * A209268 A257798 A183079

Adjacent sequences: A080995 A080996 A080997 * A080999 A081000 A081001

Keyword

nonn

Author

Matthew Vandermast, Mar 02 2003

Status

approved