A244472 2nd-largest term in n-th row of Stern's diatomic triangle A002487.

1, 2, 4, 7, 12, 19, 31, 50, 81, 131, 212, 343, 555, 898, 1453, 2351, 3804, 6155, 9959, 16114, 26073, 42187, 68260, 110447, 178707, 289154, 467861, 757015, 1224876, 1981891, 3206767, 5188658, 8395425, 13584083, 21979508, 35563591, 57543099

Offset

1,2

Links

Colin Barker, Table of n, a(n) for n = 1..1000

Jennifer Lansing, Largest Values for the Stern Sequence, J. Integer Seqs., 17 (2014), #14.7.5.

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

Formula

a(n) = A013655(n-1), n>3.

a(n) = a(n-1)+a(n-2), n>5. - Colin Barker, Jul 10 2015

G.f.: -x*(x^4+x^3+x^2+x+1) / (x^2+x-1). - Colin Barker, Jul 10 2015

Maple

A244472 := proc(n)
    if n < 4 then
        op(n, [1, 2, 4]) ;
    else
        combinat[fibonacci](n+2)-combinat[fibonacci](n-3) ;
    end if;
end proc:
seq(A244472(n), n=1..50) ; # R. J. Mathar, Jul 05 2014

Mathematica

CoefficientList[Series[-(x^4 + x^3 + x^2 + x + 1)/(x^2 + x - 1), {x, 0, 50}], x] (* Wesley Ivan Hurt, Jul 10 2015 *)
Join[{1, 2, 4}, LinearRecurrence[{1, 1}, {7, 12}, 50]] (* Vincenzo Librandi, Jul 11 2015 *)

Prog

(PARI) Vec(-x*(x^4+x^3+x^2+x+1)/(x^2+x-1) + O(x^100)) \\ Colin Barker, Jul 10 2015
(Magma) I:=[1, 2, 4, 7, 12]; [n le 5 select I[n] else Self(n-1)+Self(n-2): n in [1..40]]; // Wesley Ivan Hurt, Jul 10 2015

Crossrefs

Cf. A002487, A013655, A100545 (bisection).

Cf. A244473, A244474, A244475, A244476.

Sequence in context: A342229 A326080 A287525 * A279890 A018147 A125892

Adjacent sequences: A244469 A244470 A244471 * A244473 A244474 A244475

Keyword

nonn,easy

Author

N. J. A. Sloane, Jul 01 2014

Status

approved