M.E., from O.E. gold, from P.Gmc. *gulth-
(cf. O.H.G. gold, Ger. Gold, Du. goud, Dan. guld,
Goth. gulþ), from PIE base *ghel-/*ghol- "yellow, green;"
cf. Mod.Pers. zarr "gold," see below.

Talâ "gold," variants tala, tali. Zarr "gold;" Mid.Pers. zarr;
Av. zaranya-, zarənu- "gold;" O.Pers. daraniya- "gold;"
cf. Skt. hiranya- "gold;" also Av. zaray-, zairi- "yellow, green;"
Mod.Pers. zard "yellow;" Skt. hari- "yellow, green;"
Gk. khloe literally "young green shoot;" L. helvus "yellowish, bay;"
Rus. zeltyj "yellow;" P.Gmc. *gelwaz; Du. geel;
Ger. gelb; E. yellow.

Goldbach's conjecture

هاشن ِ گلدباخ

hâšan-e Goldbach

Fr.: conjecture de Goldbach

Every number greater than 2 is the sum of two → prime numbers.
Goldbach's number remains one of the most famous unsolved mathematical problems of today.

Named after the German mathematician Christian Goldbach (1690-1764);
→ conjecture.

golden number

عدد ِ زرّین

adad-e zarrin (#)

Fr.: nombre d'or

1) The number giving the position of any year in the lunar or
→ Metonic cycle of about 19 years.
Each year has a golden number between 1 and 19. It is found by adding
1 to the given year and dividing by 19; the remainder in the division
is the golden number. If there is no remainder the golden number
is 19 (e.g., the golden number of 2007 is 13).
2) Same as → golden ratio.

If a line segment is divided into a larger subsegment (a) and a smaller subsegment
(b), when the larger subsegment is related to the smaller exactly as the whole segment is
related to the larger segment, i.e. a/b = (a + b)/a. The golden ratio,
a/b is usually represented by the Greek letter φ. It
is also known as the divine ratio, the golden mean, the
→ golden number, and the golden section.
Its numerical value, given by the positive solution of the
equation φ^{2} - φ - 1 = 0, is
approximately 1.618033989. The golden ratio is closely related to the
→ Fibonacci sequence.

Fluid mechanics:
A second order differential equation that governs the vertical structure of
a perturbation in a stratified parallel flow.

Named after G. I. Taylor (Effect of variation in density on the stability of
superposed streams of fluid, 1931, Proc. R. Soc. Lond. A, 132, 499),
→ Taylor number, and
S. Goldstein (On the stability of superposed streams of fluids of different
densities, 1931, Proc. R. Soc. Lond. A, 132, 524);
→ equation.