This site is supported by donations to The OEIS Foundation.

 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!)
 A056676 Number of non-unitary but squarefree divisors of binomial(n,floor(n/2)). Also number of nonsquarefree but unitary divisors of binomial(n,floor(n/2)). 0

%I

%S 0,0,0,0,0,2,0,0,4,6,0,8,8,8,8,16,0,16,0,16,32,32,0,32,48,48,56,56,96,

%T 96,64,128,128,192,256,384,384,384,512,768,512,512,512,512,448,448,

%U 768,896,896,896,896,896,768,768,2048,2048,4096,4096,2048,2048,2048,2048

%N Number of non-unitary but squarefree divisors of binomial(n,floor(n/2)). Also number of nonsquarefree but unitary divisors of binomial(n,floor(n/2)).

%F a(n) = A039593(n) - A000005(A055231(x)) = A039593(n) - A000005(A007913(x)/A055229(x)), where x = A001405(n) = binomial(n, floor(n/2)).

%e n=14, C(14,7)=3432, has 32 divisors, 16 unitary, 16 squarefree. The size of overlap is 8. The complementary parts are: non-unitary/squarefree set={2,6,22,26,66,78,286,828}, while the unitary/not squarefree set of equal size is {8,24,88,104,264,312,1144,3432}. So a(14)=8.

%Y Cf. A039593, A000005, A055231, A007913, A055229, A001405.

%K nonn

%O 1,6

%A _Labos Elemer_, Aug 10 2000

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 7 20:44 EST 2019. Contains 329849 sequences. (Running on oeis4.)