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!)
A073078 Least k such that n divides C(2k,k). 2
1, 1, 2, 3, 3, 2, 4, 7, 5, 3, 6, 5, 7, 4, 8, 15, 9, 5, 10, 3, 5, 6, 12, 7, 13, 7, 14, 5, 15, 8, 16, 31, 6, 9, 4, 5, 19, 10, 7, 13, 21, 5, 22, 6, 8, 12, 24, 15, 25, 13, 11, 7, 27, 14, 8, 11, 11, 15, 30, 14, 31, 16, 5, 63, 8, 6, 34, 9, 14, 4, 36, 14, 37, 19, 14, 10, 6, 7, 40, 15, 41, 21 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(2^k)=2^k-1, if n is an odd prime a(n)=(n+1)/2 (but there are also some composites satisfying this property, see A079290).

MAPLE

A073078 := proc(n)

    for k from 1 do

        if modp(binomial(2*k, k), n) = 0 then

            return k;

        end if;

    end do:

end proc: # R. J. Mathar, Aug 20 2014

MATHEMATICA

lk[n_]:=Module[{k=1}, While[!Divisible[Binomial[2k, k], n], k++]; k]; Array[lk, 90] (* Harvey P. Dale, Oct 09 2012 *)

PROG

(PARI) a(n)=if(n<0, 0, s=1; while(binomial(2*s, s)%n>0, s++); s)

CROSSREFS

Sequence in context: A131469 A309076 A343326 * A034799 A008985 A326699

Adjacent sequences:  A073075 A073076 A073077 * A073079 A073080 A073081

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Aug 17 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 August 17 17:59 EDT 2022. Contains 356189 sequences. (Running on oeis4.)