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A226379 a(5n) = 2n(2n+1), a(5n+1) = (2n-3)(2n+5), a(5n+2) = (2n-1)(2*n+3), a(5n+3)=(2n+2)(2n+1), a(5n+4) = (2n+1)(2n+3). 0
0, -15, -3, 2, 3, 6, -7, 5, 12, 15, 20, 9, 21, 30, 35, 42, 33, 45, 56, 63, 72, 65, 77, 90, 99, 110, 105, 117, 132, 143, 156, 153, 165, 182, 195, 210, 209, 221, 240, 255, 272, 273, 285, 306, 323, 342, 345, 357, 380, 399, 420, 425, 437 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The sequence is the fifth row of the following array:

0,   6,  20, 42, 72, 110, 156, 210, 272, ...   A002943

0,   3,   6, 15, 20,  35,  42,  63,  72, ...   bisections A002943, A000466

0,   2,   3,  6, 12,  15,  20,  30,  35, ...   A226023 (trisections A002943, A000466, A002439)

0,  -3,   2,  3,  6,   5,  12,  15,  20, ...   A214297 (quadrisections A078371)

0, -15,  -3,  2,  3,   6,  -7,   5,  12, ...   a(n)

0, -63, -15, -3,  2,   3,   6, -55,  -7, ...

The principle of construction is that (i) the lower left triangular portion has constant values down the diagonals (6, 3, 2, -3, -15, ...), defined from row 4 on by the negated values of A024036. (ii) The extension along the rows is defined by maintaining bisections, trisections, quadrisections etc of the form (2*n+x)*(2*n+y) with some constants x and y. In the fifth line this needs the quintisections shown in the NAME.

Each row in the array has the subsequences of the previous row plus another subsequence of the format (2*n+1)*(2*n+y) shuffled in; the first A002943, the second also A000466, the third also A002439, the fourth also A078371, and the fifth (2*n+3)*(2*n-5).

Only the first three rows are monotonically increasing everywhere.

a(n) is divisible by A226203(n).

Numerators of: 0, -15/4, -3/4, 2/9, 3/16, 6/25, -7/36, 5/36, 12/49, 15/64, 20/81, ... = a(n)/A226096(n). A permutation of A225948(n+1)/A226008(n+1).

Is the sequence increasing monotonically from 221 on?

LINKS

Table of n, a(n) for n=0..52.

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

FORMULA

4*a(n) = A226096(n) - period 5: repeat [1, 64, 16, 1, 4].

G.f.: x*(15-12*x-5*x^2-x^3-3*x^4-17*x^5+12*x^6+3*x^7-x^8+x^9) / ( (x^4+x^3+x^2+x+1)^2 *(x-1)^3 ). - R. J. Mathar, Jun 13 2013

a(n) = a(n-1)+2*a(n-5)-2*a(n-6)-a(n-10)+a(n-11) for n > 10. - Wesley Ivan Hurt, Oct 03 2017

MATHEMATICA

CoefficientList[Series[x*(15 - 12*x - 5*x^2 - x^3 - 3*x^4 - 17*x^5 + 12*x^6 + 3*x^7 - x^8 + x^9)/((x^4 + x^3 + x^2 + x + 1)^2*(x - 1)^3), {x, 0, 80}], x] (* Wesley Ivan Hurt, Oct 03 2017 *)

CROSSREFS

Cf. A000466, A002939, A078371, A145923, A226096.

Sequence in context: A237649 A040217 A040218 * A037924 A174680 A225948

Adjacent sequences:  A226376 A226377 A226378 * A226380 A226381 A226382

KEYWORD

sign,easy

AUTHOR

Paul Curtz, Jun 05 2013

STATUS

approved

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Last modified January 23 03:15 EST 2022. Contains 350504 sequences. (Running on oeis4.)