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A064814
Greatest common divisor of n and the n-th composite number.
12
1, 2, 1, 1, 5, 6, 7, 1, 1, 2, 1, 3, 1, 2, 5, 2, 1, 2, 1, 4, 3, 2, 1, 12, 1, 13, 1, 14, 1, 15, 1, 16, 1, 2, 1, 4, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 4, 1, 10, 3, 2, 1, 2, 11, 2, 1, 1, 1, 12, 1, 2, 3, 8, 5, 1, 1, 1, 1, 5, 1, 2, 1, 2, 3, 4, 7, 2, 1, 10, 3, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 31, 1, 1, 32, 1, 2
OFFSET
1,2
COMMENTS
a(12) = gcd(12, A002808(12)) = gcd(12, 21) = gcd(2*2*3, 3*7) = 3.
LINKS
FORMULA
a(n) = gcd(n, A002808(n)).
MATHEMATICA
Composite[n_Integer] := FixedPoint[n + PrimePi[#] + 1 &, n + PrimePi[n] + 1]; Table[GCD[n, Composite[n]], {n, 100}] (* T. D. Noe, Feb 22 2012 *)
Module[{nn=150, comps}, comps=Complement[Range[2, nn], Prime[Range[ PrimePi[ nn]]]]; GCD@@@Thread[{comps, Range[Length[comps]]}]] (* Harvey P. Dale, Apr 23 2014 *)
PROG
(PARI) nextComp(n)= { if (!isprime(n), return(n)); return(n + 1) } { c=3; for (n=1, 1000, c=nextComp(c + 1); write("b064814.txt", n, " ", gcd(n, c)) ) } \\ Harry J. Smith, Sep 27 2009
CROSSREFS
Sequence in context: A210664 A176093 A092437 * A051012 A064644 A306444
KEYWORD
nice,nonn
AUTHOR
Reinhard Zumkeller, Oct 22 2001
STATUS
approved