login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A098236 Number of ways to write n as the sum of two positive distinct squarefree numbers. 3
0, 0, 1, 1, 1, 1, 2, 3, 2, 1, 2, 3, 3, 2, 3, 5, 4, 4, 3, 5, 4, 4, 4, 7, 5, 4, 5, 6, 5, 4, 5, 8, 6, 6, 6, 11, 7, 6, 7, 11, 8, 7, 9, 12, 10, 7, 8, 13, 10, 8, 7, 13, 10, 10, 7, 13, 10, 10, 9, 14, 11, 10, 11, 15, 11, 10, 11, 17, 12, 12, 11, 21, 13, 13, 13, 19, 14, 12, 14, 20, 16, 12, 13, 21 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,7

COMMENTS

Number of distinct rectangles with squarefree length and width such that L + W = n, W < L. - Wesley Ivan Hurt, Oct 29 2017

LINKS

Table of n, a(n) for n=1..84.

FORMULA

a(n) = Sum_{i=1..floor(n/2)-((n+1) mod 2)} mu(i)^2 * mu(n-i)^2. - Wesley Ivan Hurt, Oct 26 2017

MAPLE

with(numtheory): A098236:=n->add(mobius(i)^2*mobius(n-i)^2, i=1..floor(n/2)-((n+1) mod 2)): seq(A098236(n), n=1..150); # Wesley Ivan Hurt, Oct 29 2017

MATHEMATICA

Table[Sum[MoebiusMu[i]^2*MoebiusMu[n - i]^2, {i, Floor[n/2] - Mod[n + 1, 2]}], {n, 80}] (* Wesley Ivan Hurt, Oct 26 2017 *)

PROG

(PARI) a(n) = sum(i=1, n\2-(n+1)%2, moebius(i)^2*moebius(n-i)^2); \\ Michel Marcus, Oct 27 2017

CROSSREFS

Cf. A005117, A098235.

Sequence in context: A304111 A030314 A269624 * A152978 A118121 A006968

Adjacent sequences:  A098233 A098234 A098235 * A098237 A098238 A098239

KEYWORD

nonn,easy

AUTHOR

Ralf Stephan, Aug 31 2004

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 15 22:21 EDT 2018. Contains 316252 sequences. (Running on oeis4.)