OFFSET
1,1
COMMENTS
Schläfli proved that a smooth real cubic surface contains either 3, 7, 15, or 27 straight lines.
LINKS
D. Schläfli, On the distribution of surfaces of the third order into species, in reference to the absence or presence of singular points, and the reality of their lines, Philosophical Transactions of the Royal Society of London, 153 (1863), 193-241.
Kirsten Wickelgren, An Arithmetic Count of the Lines on a Smooth Cubic Surface, AMS Notices, 65 (2018), 404-405.
FORMULA
a(n) = A097080(n) = 2*n^2 - 2*n + 3 for n = 1, 2, 3, 4.
EXAMPLE
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
Jonathan Sondow, Mar 28 2018
STATUS
approved