login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A340280 Number of partitions of n into 3 parts such that the 'middle' part is relatively prime to at least one other part. 2
0, 0, 1, 1, 2, 2, 4, 4, 6, 6, 10, 8, 14, 12, 16, 16, 22, 18, 28, 24, 32, 30, 42, 32, 48, 42, 52, 48, 64, 48, 74, 64, 78, 72, 90, 72, 104, 88, 108, 96, 126, 96, 140, 118, 142, 130, 166, 128, 180, 150, 186, 164, 212, 162, 222, 190, 230, 206, 260, 192, 280, 236, 280, 252 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..64.

Index entries for sequences related to partitions

FORMULA

a(n) = Sum_{k=1..floor(n/3)} Sum_{i=k..floor((n-k)/2)} sign(floor(1/gcd(i,k)) + floor(1/gcd(i,n-i-k))).

MATHEMATICA

Table[Sum[Sum[Sign[Floor[1/GCD[k, i]] + Floor[1/GCD[i, n - i - k]]], {i, k, Floor[(n - k)/2]}], {k, Floor[n/3]}], {n, 80}]

CROSSREFS

Cf. A340279, A340282.

Sequence in context: A001310 A328422 A029009 * A340279 A343100 A023023

Adjacent sequences:  A340277 A340278 A340279 * A340281 A340282 A340283

KEYWORD

nonn

AUTHOR

Wesley Ivan Hurt, Jan 02 2021

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 28 13:05 EDT 2022. Contains 354115 sequences. (Running on oeis4.)