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A292146 Number of different convex quadrilaterals that can be formed from n congruent isosceles right triangles. Reflections are not counted as different. 2
0, 2, 2, 5, 2, 5, 3, 9, 2, 5, 2, 11, 2, 6, 4, 13, 3, 7, 2, 11, 4, 5, 3, 19, 2, 5, 4, 12, 2, 10, 3, 17, 4, 6, 4, 16, 2, 5, 4, 19, 3, 10, 2, 11, 6, 6, 3, 27, 3, 7, 4, 11, 2, 10, 4, 20, 4, 5, 2, 22, 2, 6, 7, 21, 4, 10, 2, 12, 4, 10, 3, 28, 3, 5, 6, 11, 4, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Illustrated with other convex polyabolos in A245676.

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..1000

Andrew Howroyd, Convex Quadrilaterals formed from Polyabolos

EXAMPLE

For n=2, there is a square and a parallelogram.

PROG

(PARI) \\ here b is A100073

b(n) = if(n%2, floor(numdiv(n)/2), if(n%4, 0, floor(numdiv(n/4)/2)));

d(n) = my(t); sum(k=1, floor(sqrt((n-1)/2)), issquare(n+2*k^2, &t) && t>2*k);

a(n) = 2*b(n) + d(n) + if(n%2, 0, 2*numdiv(n/2) + b(n/2)) + if(n%4, 0, ceil(numdiv(n/4)/2)); \\ Andrew Howroyd, Sep 16 2017

CROSSREFS

Strictly less than A245676.

Sequence in context: A068066 A171889 A171868 * A334685 A340694 A101910

Adjacent sequences:  A292143 A292144 A292145 * A292147 A292148 A292149

KEYWORD

nonn

AUTHOR

Douglas J. Durian, Sep 09 2017

EXTENSIONS

Terms a(33) and beyond from Andrew Howroyd, Sep 16 2017

STATUS

approved

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Last modified September 27 10:28 EDT 2021. Contains 347689 sequences. (Running on oeis4.)