The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A160545 Numbers coprime to 21. 5
 1, 2, 4, 5, 8, 10, 11, 13, 16, 17, 19, 20, 22, 23, 25, 26, 29, 31, 32, 34, 37, 38, 40, 41, 43, 44, 46, 47, 50, 52, 53, 55, 58, 59, 61, 62, 64, 65, 67, 68, 71, 73, 74, 76, 79, 80, 82, 83, 85, 86, 88, 89, 92, 94, 95, 97, 100, 101, 103, 104, 106, 107, 109, 110, 113, 115, 116 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The asymptotic density of this sequence is 4/7. - Amiram Eldar, Oct 23 2020 LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,0,0,0,0,0,1,-1). FORMULA a(n+12) = a(n) + 21. a(n) = 21*floor((n-1)/12)+f(n)+floor(f(n)/2)+2^floor(f(n)/4)+floor(((n+5) mod 12)/11)+floor(((n+3) mod 12)/11), where f(n)= (n-1) mod 12. - Gary Detlefs, Sep 22 2013 G.f.: x*(1+x+2*x^2+x^3+3*x^4+2*x^5+x^6+2*x^7+3*x^8+x^9+2*x^10+x^11+x^12) / ( (1+x) *(1+x^2) *(1+x+x^2) *(x^2-x+1) *(x^4-x^2+1) *(x-1)^2 ). - R. J. Mathar, Sep 27 2014 MATHEMATICA LinearRecurrence[{1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1}, 1, 2, 4, 5, 8, 10, 11, 13, 16, 17, 19, 20, 22}, 67] (* Ray Chandler, Jul 15 2015 *) Select[Range[100], CoprimeQ[21, #] &] (* Amiram Eldar, Oct 23 2020 *) PROG (Sage) [i for i in range(0, 128) if gcd(21, i) == 1] CROSSREFS Cf. A162699, A045572. Sequence in context: A026174 A120685 A284472 * A161790 A131396 A131391 Adjacent sequences:  A160542 A160543 A160544 * A160546 A160547 A160548 KEYWORD nonn,easy AUTHOR Zerinvary Lajos, May 18 2009 EXTENSIONS Definition corrected by Leroy Quet, Jun 19 2009 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 15 23:04 EDT 2021. Contains 343007 sequences. (Running on oeis4.)