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