A336333 Perimeter of primitive integer-sided triangles with A < B < C < 2*Pi/3 and such that FA + FB + FC is an integer where F is the Fermat point of the triangle.

195, 256, 342, 500, 490, 612, 630, 750, 972, 882, 1122, 961, 1218, 1071, 1140, 1682, 1856, 2703, 2508, 3015, 2990, 3636, 3348, 3572, 3136, 3364, 3640, 3328, 3249, 3362, 3312, 3330, 4530, 4250, 4921, 4455, 4840, 4565, 5054, 4945, 5307, 5655, 5440, 6440, 5746, 6561, 5588

Offset

1,1

Comments

Inspired by Project Euler, Problem 143 (see link).

For the corresponding primitive triples and miscellaneous properties and references, see A336328.

If FA + FB + FC = d, then we have this "beautifully symmetric equation" between a, b, c and d (see Martin Gardner):

3*(a^4 + b^4 + c^4 + d^4) = (a^2 + b^2 + c^2 + d^2)^2.

This sequence is not increasing. For example, a(4) = 500 for triangle with largest side = 205 while a(5) = 490 for triangle with largest side = 208.

References

Martin Gardner, Mathematical Circus, Elegant triangles, First Vintage Books Edition, 1979, p. 65.

Links

Table of n, a(n) for n=1..47.

Project Euler, Problem 143 - Investigating the Torricelli point of a triangle.

Formula

a(n) = A336328(n, 1) + A336328(n, 2) + A336328(n, 3).

a(n) = A336330(n) + A336331(n) + A336332(n).

Example

a(1) = 195 because the first triple is (57, 65, 73) with corresponding d = FA + FB + FC = 264/7 + 195/7 + 325/7 = 112 and 57 + 65 + 73 = 195.

Crossrefs

Cf. A336328 (triples), A336329 (FA + FB + FC), A336330 (smallest side), A336331 (middle side), A336332 (largest side), A351476, A351477.

Sequence in context: A234814 A154938 A234100 * A351803 A080394 A323975

Adjacent sequences: A336330 A336331 A336332 * A336334 A336335 A336336

Keyword

nonn

Author

Bernard Schott, Jul 21 2020

Status

approved