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A296796 Numbers k such that k is the altitude of a Heronian triangle with sides m - 11, m, m + 11. 4
12, 15, 33, 63, 72, 132, 240, 273, 495, 897, 1020, 1848, 3348, 3807, 6897, 12495, 14208, 25740, 46632, 53025, 96063, 174033, 197892, 358512, 649500, 738543, 1337985, 2423967, 2756280, 4993428, 9046368, 10286577, 18635727, 33761505, 38390028, 69549480 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(n) gives the values of y satisfying 3*x^2 - y^2 = 363; corresponding x values are given by A296795.

a(n)/3 is the radius of the inscribed circle.

LINKS

Colin Barker, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (0,0,4,0,0,-1).

FORMULA

From Colin Barker, Dec 22 2017: (Start)

G.f.: 3*(4 + 5*x + 11*x^2 + 5*x^3 + 4*x^4) / (1 - 4*x^3 + x^6).

a(n) = 4*a(n-3) - a(n-6) for n>5.

(End)

EXAMPLE

If the sides are 17, 28, 39 the triangle has the altitude 15 against 28 and is a part of the Pythagorean triangle with the sides 15, 36, 39, so 15 is a term.

MATHEMATICA

CoefficientList[Series[3 (4 + 5 x + 11 x^2 + 5 x^3 + 4 x^4)/(1 - 4 x^3 + x^6), {x, 0, 35}], x] (* Michael De Vlieger, Dec 22 2017 *)

PROG

(PARI) Vec(3*(4 + 5*x + 11*x^2 + 5*x^3 + 4*x^4) / (1 - 4*x^3 + x^6) + O(x^40)) \\ Colin Barker, Dec 22 2017

CROSSREFS

Sequence in context: A134221 A179148 A194234 * A161917 A065150 A277082

Adjacent sequences:  A296793 A296794 A296795 * A296797 A296798 A296799

KEYWORD

nonn,easy

AUTHOR

Sture Sjöstedt, Dec 20 2017

EXTENSIONS

More terms from Colin Barker, Dec 22 2017

STATUS

approved

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Last modified October 15 13:43 EDT 2018. Contains 316236 sequences. (Running on oeis4.)