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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
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
Sequence in context: A036315 A340120 A020154 * A176404 A227198 A279102
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Apr 09 2003
EXTENSIONS
a(21)-a(43) from Charles R Greathouse IV, May 24 2013
STATUS
approved