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A221966 Number of -7..7 arrays of length n with the sum ahead of each element differing from the sum following that element by 7 or less. 1
15, 225, 1695, 17025, 159615, 1535745, 14661375, 140355585, 1342437375, 12843782145, 122870296575, 1175482548225, 11245539966975, 107583628673025, 1029227717656575, 9846388295204865, 94198150438322175, 901172262043910145 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 7 of A221967.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..67

FORMULA

Empirical: a(n) = 7*a(n-1) + 32*a(n-2) - 56*a(n-3) - 160*a(n-4) + 112*a(n-5) + 256*a(n-6) - 64*a(n-7) - 128*a(n-8).

Empirical g.f.: 15*x*(1 + 2*x)*(1 - 2*x - 4*x^2)*(1 + 8*x - 16*x^2 - 8*x^3 + 16*x^4) / ((1 + x)*(1 - 2*x)*(1 + 2*x - 4*x^2)*(1 - 8*x - 16*x^2 + 8*x^3 + 16*x^4)). - Colin Barker, Aug 14 2018

EXAMPLE

Some solutions for n=6:

..1....1...-7....0....1....0....0...-7....0....0....0....0....0....1....1....1

..1....0....5....1....0....0....1....0...-4....0....0...-4....1....0....0....1

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

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

.-1...-4....1....7...-1....3...-2....3...-5....0....7...-4....1....4....6...-4

..3....3....1...-1....4...-5....4...-7....5....0...-3....0....2...-1...-2....7

CROSSREFS

Cf. A221967.

Sequence in context: A207855 A207423 A207738 * A208080 A224264 A223921

Adjacent sequences:  A221963 A221964 A221965 * A221967 A221968 A221969

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 01 2013

STATUS

approved

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Last modified December 8 18:37 EST 2019. Contains 329865 sequences. (Running on oeis4.)