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A218281 Hilltop maps: number of n X 1 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or vertical neighbor in a random 0..4 n X 1 array. 1
1, 3, 7, 15, 31, 61, 121, 241, 481, 961, 1921, 3839, 7671, 15327, 30623, 61185, 122249, 244257, 488033, 975105, 1948289, 3892739, 7777807, 15540287, 31049951, 62038717, 123955185, 247666113, 494844193, 988713281, 1975478273, 3947063807 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 1 of A218288.

LINKS

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

FORMULA

Empirical: a(n) = a(n-1) + a(n-2) + a(n-3) + a(n-4) + a(n-5) + a(n-6) + a(n-7) + a(n-8) + a(n-9).

Empirical g.f.: x*(1 + x + x^2 + x^3 + x^4)^2 / (1 - x - x^2 - x^3 - x^4 - x^5 - x^6 - x^7 - x^8 - x^9). - Colin Barker, Jul 24 2018

EXAMPLE

All solutions for n=3:

..1....0....0....1....0....1....1

..1....0....1....0....1....0....1

..1....1....1....1....0....0....0

CROSSREFS

Cf. A218288.

Sequence in context: A006778 A007574 A034480 * A057703 A006739 A119407

Adjacent sequences:  A218278 A218279 A218280 * A218282 A218283 A218284

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 25 2012

STATUS

approved

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Last modified January 19 14:53 EST 2020. Contains 331049 sequences. (Running on oeis4.)