A184418 Convolution square of A040001.

1, 2, 5, 6, 10, 10, 15, 14, 20, 18, 25, 22, 30, 26, 35, 30, 40, 34, 45, 38, 50, 42, 55, 46, 60, 50, 65, 54, 70, 58, 75, 62, 80, 66, 85, 70, 90, 74, 95, 78, 100, 82, 105, 86, 110, 90, 115, 94, 120, 98, 125, 102, 130, 106, 135, 110, 140, 114, 145, 118, 150, 122, 155, 126

Offset

0,2

Links

G. C. Greubel, Table of n, a(n) for n = 0..10000

Michael Somos, Rational Function Multiplicative Coefficients

Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).

Formula

G.f.: (1 + x + x^2)^2 / (1 - x^2)^2 = 1 + x * (x + 2) * (2*x + 1) / (1 - x^2)^2. a(-n) = -a(n) except a(0) = 2.

Euler transform of length 3 sequence [2, 2, -2].

a(n) = 2 * b(n) where b() is multiplicative with b(2^e) = 5 * 2^(e-2) if e>0, b(p^e) = p^e if p>2.

a(2*n + 1) = 4*n + 2, a(2*n) = 5*n except a(0) = 2.

a(n) = (9+(-1)^n)*n/4 = (n/2)*A010710(n+1) for n>0. - Bruno Berselli, Mar 24 2011

Example

G.f. = 1 + 2*x + 5*x^2 + 6*x^3 + 10*x^4 + 10*x^5 + 15*x^6 + 14*x^7 + 20*x^8 + ...

Mathematica

LinearRecurrence[{0, 2, 0, -1}, {1, 2, 5, 6, 10}, 80] (* Harvey P. Dale, Jul 03 2017 *)

Prog

(PARI) {a(n) = (n==0) + n * ([5/2, 2] [n%2 + 1])};
(PARI) {a(n) = if( n==0, 1, sign(n) * polcoeff( (1 + x + x^2)^2 / (1 - x^2)^2 + x * O(x^abs(n)), abs(n)))};
(Magma) I:=[2, 5, 6, 10]; [1] cat [n le 4 select I[n] else 2*Self(n-2) - Self(n-4): n in [1..30]]; // G. C. Greubel, Aug 14 2018

Crossrefs

Sequence in context: A295741 A007503 A337298 * A112967 A244731 A307562

Adjacent sequences: A184415 A184416 A184417 * A184419 A184420 A184421

Keyword

nonn

Author

Michael Somos, Feb 14 2011

Status

approved