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A245489 a(n) = (1^n + (-2)^n + 4^n)/3. 2
1, 1, 7, 19, 91, 331, 1387, 5419, 21931, 87211, 349867, 1397419, 5593771, 22366891, 89483947, 357903019, 1431677611, 5726579371, 22906579627, 91625794219, 366504225451, 1466014804651, 5864063412907, 23456245263019, 93824997829291, 375299957762731 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (3,6,-8).

FORMULA

G.f.: (1 - 2*x - 2*x^2) / ((1 - x) * (1 + 2*x) * (1 - 4*x)).

0 = 8*a(n) - 6*a(n+1) - 3*a(n+2) + a(n+3) for all n in Z.

a(2*n) = A090596(4*n + 3). a(2*n + 1) = A129362(4*n).

a(n) = A001045(3*n)/(3*A001045(n)) for n >= 1. - Peter Bala, Apr 06 2015

E.g.f.: (exp(x) + exp(4*x) + exp(-2*x))/3. - G. C. Greubel, Sep 21 2019

EXAMPLE

G.f. = 1 + x + 7*x^2 + 19*x^3 + 91*x^4 + 331*x^5 + 1387*x^6 + 5419*x^7 + ...

MAPLE

seq((1 +(-2)^n +4^n)/3, n=0..30); # G. C. Greubel, Sep 21 2019

MATHEMATICA

CoefficientList[Series[(1-2x-2x^2)/((1-x)(1+2x)(1-4x)), {x, 0, 40}], x] (* Vincenzo Librandi, Jul 25 2014 *)

LinearRecurrence[{3, 6, -8}, {1, 1, 7}, 30] (* Harvey P. Dale, Dec 04 2018 *)

PROG

(PARI) {a(n) = (1^n + (-2)^n + 4^n) / 3};

(PARI) {a(n) = if( n<0, 4^n, 1) * polcoeff( (1 - 2*x - 2*x^2) / ((1 - x) * (1 + 2*x) * (1 - 4*x)) + x * O(x^abs(n)), abs(n))};

(MAGMA) [(1^n + (-2)^n + 4^n) / 3 : n in [0..30]]; // Vincenzo Librandi, Jul 25 2014

(Sage) [(1 +(-2)^n +4^n)/3 for n in (0..30)] # G. C. Greubel, Sep 21 2019

(GAP) List([0..30], n-> (1 +(-2)^n +4^n)/3); # G. C. Greubel, Sep 21 2019

CROSSREFS

Cf. A001045, A090596, A129362.

Sequence in context: A088988 A109879 A109880 * A084603 A088883 A262186

Adjacent sequences:  A245486 A245487 A245488 * A245490 A245491 A245492

KEYWORD

nonn,easy

AUTHOR

Michael Somos, Jul 23 2014

STATUS

approved

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Last modified December 7 20:23 EST 2019. Contains 329847 sequences. (Running on oeis4.)