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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A308061 Number of integer-sided triangles with perimeter n whose side lengths are squarefree. 5
0, 0, 1, 0, 1, 1, 2, 1, 1, 0, 2, 1, 3, 2, 5, 3, 3, 2, 2, 1, 3, 3, 6, 4, 3, 2, 6, 4, 7, 7, 11, 8, 8, 6, 11, 8, 9, 6, 13, 9, 10, 6, 13, 9, 16, 12, 20, 15, 17, 12, 15, 10, 16, 14, 15, 11, 12, 10, 16, 12, 18, 18, 25, 19, 21, 19, 26, 19, 29, 27, 35, 27, 29, 27 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,7

LINKS

Table of n, a(n) for n=1..74.

FORMULA

a(n) = Sum_{k=1..floor(n/3)} Sum_{i=k..floor((n-k)/2)} sign(floor((i+k)/(n-i-k+1))) * mu(i)^2 * mu(k)^2 * mu(n-i-k)^2, where mu is the Möbius function (A008683).

MATHEMATICA

Table[Sum[Sum[MoebiusMu[i]^2*MoebiusMu[k]^2*MoebiusMu[n - i - k]^2*Sign[Floor[(i + k)/(n - i - k + 1)]], {i, k, Floor[(n - k)/2]}], {k, Floor[n/3]}], {n, 100}]

CROSSREFS

Cf. A005044, A008683.

Sequence in context: A029375 A071462 A101979 * A060582 A060450 A180918

Adjacent sequences:  A308058 A308059 A308060 * A308062 A308063 A308064

KEYWORD

nonn,easy

AUTHOR

Wesley Ivan Hurt, May 10 2019

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 December 16 01:43 EST 2019. Contains 330013 sequences. (Running on oeis4.)