This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A047390 Numbers that are congruent to {0, 3, 5} mod 7. 1
 0, 3, 5, 7, 10, 12, 14, 17, 19, 21, 24, 26, 28, 31, 33, 35, 38, 40, 42, 45, 47, 49, 52, 54, 56, 59, 61, 63, 66, 68, 70, 73, 75, 77, 80, 82, 84, 87, 89, 91, 94, 96, 98, 101, 103, 105, 108, 110, 112, 115, 117, 119, 122, 124, 126, 129, 131, 133, 136, 138, 140, 143 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers k such that k*(k+2)*(k+4) is divisible by 7. - Bruno Berselli, Dec 28 2017 LINKS Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1). FORMULA a(n) = 2*n + floor(n/3) + (n^2 mod 3), with offset 0, a(0)=0. - Gary Detlefs, Mar 19 2010 From Bruno Berselli, Mar 29 2011: (Start) G.f.: x^2*(3 + 2*x + 2*x^2)/((1 - x)^2*(1 + x + x^2)). a(n) = (1/3)*(7*n - 6 - A049347(n-1)) = A047391(n) - A079978(n-1). (End) a(n) = n + ceiling(4*(n-1)/3) - 1. - Arkadiusz Wesolowski, Sep 18 2012 a(n) = 2*(n-1) + ceiling((n-1)/3). - Karl V. Keller, Jr., Nov 01 2014 From Wesley Ivan Hurt, Jun 10 2016: (Start) a(n) = a(n-1) + a(n-3) - a(n-4) for n>4. a(n) = 7*n/3 - 2 - 2*sin(2*n*Pi/3)/(3*sqrt(3)). a(3*k) = 7*k-2, a(3*k-1) = 7*k-4, a(3*k-2) = 7*k-7. (End) MAPLE seq(2*n+floor(n/3)+(n^2 mod 3), n=0..52); # Gary Detlefs, Mar 19 2010 MATHEMATICA Select[Range[0, 150], MemberQ[{0, 3, 5}, Mod[#, 7]]&] (* Harvey P. Dale, Dec 07 2011 *) CoefficientList[Series[x (3 + 2 x + 2 x^2)/((1 - x)^2 (1 + x + x^2)), {x, 0, 70}], x] (* Vincenzo Librandi, Nov 02 2014 *) PROG (MAGMA) [n: n in [0..122] | n mod 7 in [0, 3, 5]];  // Bruno Berselli, Mar 29 2011 (Python) import math a = lambda n: 2*(n-1)+math.ceil((n-1)/3.0) for n in range(1, 101): print(a(n), end = ", ") # Karl V. Keller, Jr., Nov 01 2014 (PARI) is(n)=!!setsearch([0, 3, 5], n%7) \\ Charles R Greathouse IV, Nov 09 2014 (PARI) a(n)=(7*n-5)\3 \\ Charles R Greathouse IV, Nov 09 2014 CROSSREFS Cf. A011655, A047391, A049347, A079978. Sequence in context: A190511 A260466 A033035 * A184653 A263085 A206334 Adjacent sequences:  A047387 A047388 A047389 * A047391 A047392 A047393 KEYWORD nonn,easy AUTHOR 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 August 25 16:17 EDT 2019. Contains 326324 sequences. (Running on oeis4.)