A026474 a(n) = least positive integer > a(n-1) and not equal to a(i)+a(j) or a(i)+a(j)+a(k) for 1<=i<j<k<n (a 3-Stohr sequence).

1, 2, 4, 8, 15, 22, 29, 36, 43, 50, 57, 64, 71, 78, 85, 92, 99, 106, 113, 120, 127, 134, 141, 148, 155, 162, 169, 176, 183, 190, 197, 204, 211, 218, 225, 232, 239, 246, 253, 260, 267, 274, 281, 288, 295, 302, 309, 316, 323, 330, 337, 344, 351, 358, 365, 372

Offset

1,2

Comments

All h-Stohr sequences have formula: h terms 1,2,..,2^(n-1),..,2^(h-1) and then continue (2^h-1)(n-h)+1. - Henry Bottomley, Feb 04 2000

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Stoehr Sequence.

Index entries for linear recurrences with constant coefficients, signature (2,-1).

Formula

Starts 1, 2, 4 then the numbers 7*(n-3)+1.

a(n) = 7*n-20 for n>3. a(n) = 2*a(n-1)-a(n-2) for n>5. G.f.: x*(1+x^2+2*x^3+3*x^4)/(1-x)^2. - Colin Barker, Sep 19 2012

Mathematica

Join[{1, 2, 4, 8}, Range[15, 500, 7]] (* Vladimir Joseph Stephan Orlovsky, Jan 27 2012 *)
CoefficientList[Series[(1 + x^2 + 2 x^3 + 3 x^4)/(1 - x)^2, {x, 0, 60}], x] (* Vincenzo Librandi, Oct 18 2013 *)
LinearRecurrence[{2, -1}, {1, 2, 4, 8, 15}, 60] (* Harvey P. Dale, May 14 2018 *)

Prog

(Magma) [1, 2, 4] cat [7*n+1: n in [1..60]]; // Vincenzo Librandi, Oct 18 2013
(PARI) a(n)=if(n>3, 7*n-20, 2^(n-1)) \\ Charles R Greathouse IV, Sep 17 2015

Crossrefs

Cf. A026472, A026476, A033627, A051039, A051040.

Sequence in context: A288313 A213020 A279858 * A301629 A339507 A305992

Adjacent sequences: A026471 A026472 A026473 * A026475 A026476 A026477

Keyword

nonn,easy,changed

Author

Clark Kimberling

Extensions

More terms from Eric W. Weisstein

Status

approved