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A079290 Composite numbers satisfying A073078(n)=(n+1)/2. 3
9, 15, 25, 27, 49, 81, 121, 125, 169, 243, 289, 343, 361, 529, 625, 729, 841, 961, 1331, 1369, 1681, 1849, 2187, 2197, 2209, 2401, 2809, 3125, 3481, 3721, 4489, 4913, 5041, 5329, 6241, 6561, 6859, 6889, 7921, 9409, 10201, 10609, 11449 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..94

MAPLE

A073078 := proc(n)

    local bink, k ;

    bink := 1 ;

    for k from 1 do

        bink := 2*bink*(2-1/k) ;

        if modp(bink, n) = 0 then

            return k;

        end if;

    end do:

end proc:

A079290 := proc(n)

    option remember;

    local a;

    if n = 1 then

        9;

    else

        for a from procname(n-1)+1 do

            if not isprime(a) and 2*A073078(a) = a+1 then

                return a;

            end if;

        end do:

    end if;

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

MATHEMATICA

b[n_] := For[k=1, True, k++, If[Divisible[Binomial[2k, k], n], Return[k]]];

Select[Select[Range[12000], CompositeQ], b[#] == (# + 1)/2&] (* Jean-François Alcover, Oct 31 2019 *)

PROG

(PARI) p=5; forprime(q=7, 1e4, forstep(n=p+2, q-2, 2, for(s=2, n\2, if(binomial(2*s, s)%n==0, next(2))); print1(n", ")); p=q) \\ Charles R Greathouse IV, May 24 2013

CROSSREFS

Cf. A073078.

Sequence in context: A337237 A036315 A020154 * A176404 A227198 A279102

Adjacent sequences:  A079287 A079288 A079289 * A079291 A079292 A079293

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Apr 09 2003

EXTENSIONS

a(21)-a(43) from Charles R Greathouse IV, May 24 2013

STATUS

approved

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Last modified September 26 02:28 EDT 2020. Contains 337346 sequences. (Running on oeis4.)