1,2

A permutation of sequence A018804, which gives the sum of gcd (k,n) for 1 <= k <= n.

The multiplicative formula for the numerator in a positive integer's centrality fraction is: for prime p, a(p^e)= p^(e-1)*((p-1)e+p) (cf. A018804). Dividing by the square of the integer gives the integer's centrality, which is defined to be the average fraction of the integer that it shares with the other integers as a gcd; see A080997 for other interpretations. This sequence gives the unreduced centrality numerators for A080997(n), where A080997 is the sequence of positive integers in nonincreasing order of their centrality.

Cf. A080997, A080998 for centrality rankings of the positive integers.

Adjacent sequences: A080996 A080997 A080998 this_sequence A081000 A081001 A081002

Sequence in context: A072655 A108301 A095290 this_sequence A077579 A076797 A052977

nonn

Matthew Vandermast (ghodges14(AT)comcast.net), Mar 02 2003