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A187601 n/2 times period 6 sequence [1, 2, 3, 4, 3, 2, ...]. 2
0, 1, 3, 6, 6, 5, 3, 7, 12, 18, 15, 11, 6, 13, 21, 30, 24, 17, 9, 19, 30, 42, 33, 23, 12, 25, 39, 54, 42, 29, 15, 31, 48, 66, 51, 35, 18, 37, 57, 78, 60, 41, 21, 43, 66, 90, 69, 47, 24, 49, 75, 102, 78, 53, 27, 55, 84, 114, 87, 59, 30, 61, 93, 126, 96, 65, 33, 67, 102 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

A007310 is a subsequence.

LINKS

Bruno Berselli, Table of n, a(n) for n = 0..5000

Index entries for linear recurrences with constant coefficients, signature (2,-1,-2,4,-2,-1,2,-1).

FORMULA

a(n) = (n/2)*A028356(n).

G.f.: x*(1+x+x^2-x^3+x^4+x^5+x^6)/((1-x)^2*(1+x)^2*(1-x+x^2)^2).

a(-n) = -a(n).  a(n) =  2*a(n-1)-a(n-2)-2*a(n-3)+4*a(n-4)-2*a(n-5)-a(n-6)+2*a(n-7)-a(n-8) for n>7.

a(n) = n*(5-2*(-1)^floor((n+1)/3)-(-1)^n)/4.

MATHEMATICA

CoefficientList[Series[x (1 + x + x^2 - x^3 + x^4 + x^5 + x^6) / ((1 - x)^2 (1 + x)^2 (1 - x + x^2)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Aug 19 2013 *)

LinearRecurrence[{2, -1, -2, 4, -2, -1, 2, -1}, {0, 1, 3, 6, 6, 5, 3, 7}, 90] (* Harvey P. Dale, Aug 20 2017 *)

PROG

(MAGMA)  [(n/2)*[1, 2, 3, 4, 3, 2][n mod 6 + 1]: n in [0..68]]; /* Other: */ [n*(5-2*(-1)^Floor((n+1)/3)-(-1)^n)/4: n in [0..68]];

CROSSREFS

Cf. A186813.

Cf. A109044, A088439 (by Superseeker).

Sequence in context: A074785 A225462 A179949 * A113737 A292165 A327576

Adjacent sequences:  A187598 A187599 A187600 * A187602 A187603 A187604

KEYWORD

nonn,look,easy

AUTHOR

Bruno Berselli, Mar 11 2011

STATUS

approved

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Last modified September 23 20:42 EDT 2021. Contains 347617 sequences. (Running on oeis4.)