Logo

Greetings from The On-Line Encyclopedia of Integer Sequences!

Hints

Search: id:A123709
Displaying 1-1 of 1 results found. page 1
     Format: long | short | internal | text      Sort: relevance | references | number      Highlight: on | off
A123709 a(n) = number of nonzero elements in row n of triangle A123706. +0
7
1, 2, 3, 4, 3, 4, 3, 4, 4, 6, 3, 8, 3, 6, 7, 4, 3, 8, 3, 8, 7, 6, 3, 8, 4, 6, 4, 8, 3, 11, 3, 4, 7, 6, 7, 8, 3, 6, 7, 8, 3, 11, 3, 8, 8, 6, 3, 8, 4, 8, 7, 8, 3, 8, 7, 8, 7, 6, 3, 16, 3, 6, 8, 4, 7, 12, 3, 8, 7, 14, 3, 8, 3, 6, 8, 8, 7, 12, 3, 8, 4, 6, 3, 16, 7, 6, 7, 8, 3, 16, 7, 8, 7, 6, 7, 8, 3, 8, 8, 8, 3, 12 (list; graph; listen)
OFFSET

1,2

COMMENT

Triangle A123706 is the matrix inverse of triangle A010766, where A010766(n,k) = [n/k]. a(n) = 4 when n is in A123710. a(n) = 8 when n is in A123711. a(n) = 16 when n is in A123712.

FORMULA

a(n) = 2^(m+1) - 1 when n is an odd number with exactly m distinct prime factors.

EXAMPLE

a(n) = 3 when n is an odd prime.

a(n) = 7 when n is an odd number with exactly 2 distinct prime factors (A046388).

a(n) = 15 when n is an odd number with exactly 3 distinct prime factors (A046389).

PROGRAM

(PARI) {a(n)=local(M=matrix(n, n, r, c, if(r>=c, floor(r/c)))^-1); sum(k=1, n, if(M[n, k]==0, 0, 1))}

CROSSREFS

Cf. A123706, A123707, A123708, A123710, A123711, A123712; A010766.

Sequence in context: A106826 A139048 A158515 this_sequence A165482 A099034 A165576

Adjacent sequences: A123706 A123707 A123708 this_sequence A123710 A123711 A123712

KEYWORD

nonn

AUTHOR

Paul D. Hanna (pauldhanna(AT)juno.com), Oct 09 2006

page 1

Search completed in 0.002 seconds

Lookup | Welcome | Find friends | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
More pages | Superseeker | Maintained by N. J. A. Sloane (njas@research.att.com)

Last modified November 30 13:13 EST 2009. Contains 167758 sequences.


AT&T Labs Research