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A329404 Interleave 2*n*(3*n-1), (2*n+1)*(6*n+1) for n >= 0. 1
0, 1, 4, 21, 20, 65, 48, 133, 88, 225, 140, 341, 204, 481, 280, 645, 368, 833, 468, 1045, 580, 1281, 704, 1541, 840, 1825, 988, 2133, 1148, 2465, 1320, 2821, 1504, 3201, 1700, 3605, 1908, 4033, 2128, 4485, 2360, 4961 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) + a(n+3) = 21, 21, 69, 69, 153, 153, ...

Hexagonal spiral for A026741:

.

                   33--17--35--18

                   /

                 16   8--17---9--19

                 /   /             \

               31  15   5---3---7  10

               /   /   /         \   \

             15   7   2   0===1===4==21==>

               \   \   \     /   /   /

               29  13   3---1   9  11

                 \   \         /   /

                 14   6--11---5  23

                   \             /

                   27--13--25--12

.

a(n) is the horizontal sequence from 0.

LINKS

Colin Barker, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (0,3,0,-3,0,1).

FORMULA

a(n) = n * A165355(n-1).

From Colin Barker, Nov 13 2019: (Start)

G.f.: x*(1 + 4*x + 18*x^2 + 8*x^3 + 5*x^4) / ((1 - x)^3*(1 + x)^3).

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

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

(End)

PROG

(PARI) concat(0, Vec(x*(1 + 4*x + 18*x^2 + 8*x^3 + 5*x^4) / ((1 - x)^3*(1 + x)^3) + O(x^45))) \\ Colin Barker, Nov 13 2019

CROSSREFS

Cf. A005449, A014641, A026741, A033579, A165355.

Sequence in context: A202450 A144292 A338421 * A076943 A138228 A303722

Adjacent sequences:  A329401 A329402 A329403 * A329405 A329406 A329407

KEYWORD

nonn,easy

AUTHOR

Paul Curtz, Nov 13 2019

STATUS

approved

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Last modified June 22 12:43 EDT 2021. Contains 345380 sequences. (Running on oeis4.)