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

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 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. 11

%I

%S 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,

%T 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,

%U 10,11,15,11,10,11,17,12,12,11,21,13,13,13,19,14,12,14,20,16,12,13,21

%N Number of ways to write n as the sum of two positive distinct squarefree numbers.

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

%F 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

%p 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

%t 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 *)

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

%Y Cf. A005117, A098235.

%K nonn,easy

%O 1,7

%A _Ralf Stephan_, Aug 31 2004

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.

Last modified December 5 12:24 EST 2021. Contains 349557 sequences. (Running on oeis4.)