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!)
A073840 Product of the composite numbers between n and 2n (both inclusive). 2
1, 4, 24, 192, 4320, 51840, 120960, 29030400, 65318400, 145152000, 6706022400, 160944537600, 8717829120000, 6590678814720000, 14122883174400000, 30128817438720000, 2112783322890240000, 2662106986841702400000 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
a(n) is divisible by central binomial coefficients, A001405[n]
LINKS
FORMULA
a(n)=A049614(2n)/A049614(n-1)
EXAMPLE
a(6) = 6*8*9*10*12 = 51840.
MAPLE
for n from 1 to 50 do l := 1:for j from n to 2*n do if not isprime(j) then l := l*j:fi:od:a[n] := l:od:seq(a[j], j=1..50);
MATHEMATICA
cs[x_] := Flatten[Position[Table[PrimeQ[j], {j, x, 2*x}], False]]+x-1; prcs[x_] := Apply[Times, cs[x]]; Table[prcs[w], {w, 1, 25}]
PROG
(PARI) a(n)=prod(i=n, 2*n, i^if(isprime(i), 0, 1))
CROSSREFS
Sequence in context: A293021 A002866 A182798 * A024249 A007145 A241000
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Aug 13 2002
EXTENSIONS
More terms from Sascha Kurz and Labos Elemer, Aug 14 2002
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 March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)