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A246480 Number of length 1+3 0..n arrays with no pair in any consecutive four terms totalling exactly n. 1
2, 10, 60, 172, 462, 966, 1880, 3256, 5370, 8290, 12372, 17700, 24710, 33502, 44592, 58096, 74610, 94266, 117740, 145180, 177342, 214390, 257160, 305832, 361322, 423826, 494340, 573076, 661110, 758670, 866912, 986080, 1117410, 1261162 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 3*a(n-1) - a(n-2) - 5*a(n-3) + 5*a(n-4) + a(n-5) - 3*a(n-6) + a(n-7).

Conjectures from Colin Barker, Nov 06 2018: (Start)

G.f.: 2*x*(1 + 2*x + 16*x^2 + 6*x^3 + 23*x^4) / ((1 - x)^5*(1 + x)^2).

a(n) = -n + 3*n^2 - 2*n^3 + n^4 for n even.

a(n) = -3 + 3*n + 3*n^2 - 2*n^3 + n^4 for n odd.

(End)

EXAMPLE

Some solutions for n=6:

..6....4....6....1....4....4....1....5....4....0....2....1....1....4....0....5

..3....1....5....4....5....0....0....3....4....4....2....2....3....4....4....5

..5....4....5....0....0....5....3....5....3....3....1....3....2....6....5....5

..2....4....2....4....5....5....4....5....5....5....0....2....0....4....5....5

CROSSREFS

Row 1 of A246479.

Sequence in context: A240605 A095993 A029725 * A303361 A026161 A025188

Adjacent sequences:  A246477 A246478 A246479 * A246481 A246482 A246483

KEYWORD

nonn

AUTHOR

R. H. Hardin, Aug 27 2014

STATUS

approved

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Last modified December 5 03:31 EST 2020. Contains 338943 sequences. (Running on oeis4.)