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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A201050 C(n#, (n-1)#), where n# is the primorial A034386(n), the product of primes <= n. 0
 1, 2, 15, 1, 593775, 1, 1985871372366807082113118777430351536, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Next term a(11) has 305 digits. a(n) = 1 if and only if n is nonprime. When n is composite, n# and (n-1)# are the same, and since C(n, n) = 1, a(n) = 1 as well. LINKS Table of n, a(n) for n=1..10. FORMULA a(n) = binomial(n#, (n-1)#). a(n) = n^A010051(n)*binomial(n# - 1, (n-1)# - 1). - Arkadiusz Wesolowski, Oct 21 2013 EXAMPLE a(3) = 15 because the 3rd primorial is 6, the (3-1)th primorial is 2, and C(6, 2) = 15. a(5) = (product_{i=5#-3#+1..5#} a(i))/(3#)! = 25*26*27*28*29*30/6! = 593775. MATHEMATICA lst = {}; Do[AppendTo[lst, Binomial[Product[Prime[i], {i, n}], Product[Prime[i], {i, n - 1}]]]; AppendTo[lst, Table[1, {Prime[n + 1] - Prime[n] - 1}]], {n, 6}]; Prepend[Flatten[lst], 1] PROG (PARI) a(n)=my(k=prod(i=1, primepi(n), prime(i))); binomial(k, k/n) \\ Charles R Greathouse IV, Nov 30 2011 CROSSREFS Cf. A034386. Sequence in context: A027739 A193307 A331511 * A299321 A248537 A352000 Adjacent sequences: A201047 A201048 A201049 * A201051 A201052 A201053 KEYWORD nonn AUTHOR Arkadiusz Wesolowski, Nov 26 2011 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.

Last modified February 21 12:33 EST 2024. Contains 370235 sequences. (Running on oeis4.)