login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A068067 Number of integers m, 0 < m <= n, such that n divides m(m+1)/2. 2
1, 0, 2, 0, 2, 1, 2, 0, 2, 1, 2, 1, 2, 1, 4, 0, 2, 1, 2, 1, 4, 1, 2, 1, 2, 1, 2, 1, 2, 3, 2, 0, 4, 1, 4, 1, 2, 1, 4, 1, 2, 3, 2, 1, 4, 1, 2, 1, 2, 1, 4, 1, 2, 1, 4, 1, 4, 1, 2, 3, 2, 1, 4, 0, 4, 3, 2, 1, 4, 3, 2, 1, 2, 1, 4, 1, 4, 3, 2, 1, 2, 1, 2, 3, 4, 1, 4, 1, 2, 3, 4, 1, 4, 1, 4, 1, 2, 1, 4, 1, 2, 3, 2, 1, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(n) = 0 iff n = 2^k with k >= 1.

Least n with a(n) = 2^k is p(k+1)#/2 = A002110(A000040(k+1))/2. Least n with a(n) = 2^k-1 != 1 is p(k+1)#.

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000

FORMULA

If n is even, a(n) = 2^(omega(n)-1) - 1; if n is odd, a(n) = 2^omega(n). Here omega(n) = A001221(n) is the number of distinct prime divisors of n.

A068068(n) - a(n) = 0 if n is odd, 1 if n is even.

MATHEMATICA

a[n_] := Length[Select[Range[n], Mod[ #(#+1)/2, n]==0&]]

CROSSREFS

Cf. A068068.

Sequence in context: A260803 A260804 A341345 * A046926 A200815 A074398

Adjacent sequences:  A068064 A068065 A068066 * A068068 A068069 A068070

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Feb 18 2002

EXTENSIONS

Edited by David W. Wilson and Dean Hickerson, Jun 08 2002

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 8 13:25 EST 2021. Contains 341948 sequences. (Running on oeis4.)