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A134536
a(n) = gcd(c(n), c(2n)), where c(n) is the n-th composite positive integer.
1
2, 3, 4, 3, 2, 3, 2, 1, 4, 2, 2, 3, 1, 6, 5, 2, 1, 4, 5, 1, 3, 1, 5, 4, 2, 1, 4, 6, 1, 3, 2, 8, 7, 1, 1, 2, 2, 1, 2, 1, 2, 5, 1, 7, 1, 1, 1, 4, 1, 7, 9, 2, 3, 1, 1, 3, 10, 9, 1, 2, 5, 2, 3, 8, 10, 1, 1, 3, 2, 1, 1, 1, 9, 4, 3, 2, 3, 1, 1, 1, 1, 4, 2, 1, 2, 1, 2, 1, 12, 11, 2, 1, 2, 1, 2, 2, 1, 10, 11, 1, 2, 5
OFFSET
1,1
LINKS
MAPLE
A002808 := proc(n) option remember ; local a; if n = 1 then 4; else for a from A002808(n-1)+1 do if not isprime(a) then RETURN(a) ; fi ; od: fi ; end: A134536 := proc(n) gcd( A002808(n), A002808(2*n)) ; end: seq(A134536(n), n=1..120) ; # R. J. Mathar, Feb 05 2008
MATHEMATICA
Composite[n_] := FixedPoint[n + PrimePi[#] + 1&, n + PrimePi[n] + 1];
a[n_] := GCD[Composite[n], Composite[2n]];
Table[a[n], {n, 1, 102}] (* Jean-François Alcover, Jan 28 2024 *)
PROG
(Magma) v:=[k:k in [2..300]|not IsPrime(k)]; [Gcd(v[m], v[2*m]):m in [1..101]]; // Marius A. Burtea, Aug 03 2019
CROSSREFS
Cf. A002808.
Sequence in context: A030340 A122453 A017849 * A214551 A371769 A343435
KEYWORD
nonn
AUTHOR
Leroy Quet, Jan 31 2008
EXTENSIONS
More terms from R. J. Mathar, Feb 05 2008
STATUS
approved