The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A132740 Largest divisor of n coprime to 10. 15
 1, 1, 3, 1, 1, 3, 7, 1, 9, 1, 11, 3, 13, 7, 3, 1, 17, 9, 19, 1, 21, 11, 23, 3, 1, 13, 27, 7, 29, 3, 31, 1, 33, 17, 7, 9, 37, 19, 39, 1, 41, 21, 43, 11, 9, 23, 47, 3, 49, 1, 51, 13, 53, 27, 11, 7, 57, 29, 59, 3, 61, 31, 63, 1, 13, 33, 67, 17, 69, 7, 71, 9, 73, 37, 3, 19, 77, 39, 79, 1, 81 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Or: n with all factors of 2 and 5 removed. - M. F. Hasler, Apr 25 2017 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A000265(A132739(n)) = A132739(A000265(n)) = n / A132741(n); A051626(a(n)) = A051626(n); A007732(a(n)) = A007732(n); a(A003592(n)) = 1. Multiplicative with a(2^e) = 1, a(5^e) = 1 and a(p^e) = p^e for p = 3 and p >= 7. Dirichlet g.f. zeta(s-1)*(2^s-2)*(5^s-5)/((2^s-1)*(5^s-1)). - R. J. Mathar, Sep 06 2011 Sum_{k=1..n} a(k) ~ (5/18) * n^2. - Amiram Eldar, Nov 28 2022 EXAMPLE a(1050) = a(2*3*5*5*7) = 3*7 = 21. MAPLE A132740 := proc(n) n/A132741(n) ; end proc: # R. J. Mathar, Sep 06 2011 MATHEMATICA a[n_] := FixedPoint[ Quotient[#, GCD[#, 10]]& , n]; Table[a[n], {n, 1, 81}] (* Jean-François Alcover, Sep 06 2011, after Vladimir Joseph Stephan Orlovsky *) Table[SelectFirst[Reverse[Divisors[n]], CoprimeQ[#, 10]&], {n, 90}] (* Uses the SelectFirst function from Mathematica version 10. - Harvey P. Dale, Mar 22 2015 *) a[n_] := n / Times @@ ({2, 5}^IntegerExponent[n, {2, 5}]); Array[a, 100] (* Amiram Eldar, Jun 12 2022 *) PROG (Haskell) a132740 = a132739 . a000265 -- Reinhard Zumkeller, Apr 08 2011 (PARI) a(n)=n/5^valuation(n, 5)>>valuation(n, 2) \\ Charles R Greathouse IV, Sep 06 2011 CROSSREFS Cf. A000265, A003592, A069105, A070021, A070022, A070023, A132739, A132741. Sequence in context: A140211 A248101 A097706 * A106621 A011085 A199922 Adjacent sequences: A132737 A132738 A132739 * A132741 A132742 A132743 KEYWORD nonn,mult,easy AUTHOR Reinhard Zumkeller, Aug 27 2007 EXTENSIONS Edited by M. F. Hasler, Apr 25 2017 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.

Last modified March 31 21:40 EDT 2023. Contains 361673 sequences. (Running on oeis4.)