login
A238822
Number of equilateral triangles bounded by the sides and diagonals of a regular 3n-gon.
1
1, 14, 69, 188, 465, 882, 1645, 2648, 4257, 6170, 9141, 12564, 17329, 22778, 30045, 38192, 48705, 60318, 74917, 90740, 110481, 131714, 157389, 184968, 217825, 252902, 294165, 337988, 388977, 442710, 505021, 570464, 645249, 723758, 812805, 906012, 1011025, 1120658, 1243437, 1371080
OFFSET
1,2
LINKS
Antreas Hatzipolakis and Giovanni Resta, Number of Equilateral Triangles in Regular 3n-gon, Postings to the Sequence Fans Mailing List, Apr 08 2013
Andrew Howroyd, PARI Program, Sep 2024.
FORMULA
Conjecture: For odd n, a(n) = n*(n+1)^3/2 - 3*n^2. - Vilim Lendvaj, Jul 24 2024
CROSSREFS
Cf. A006561.
Sequence in context: A075480 A236164 A254004 * A244943 A347673 A249708
KEYWORD
nonn,nice
AUTHOR
N. J. A. Sloane, Mar 07 2014
EXTENSIONS
a(6)-a(24) from Luca Petrone, Mar 28 2017
Corrected and extended by Vilim Lendvaj, Jul 24 2024
a(26) onwards from Andrew Howroyd, Sep 26 2024
STATUS
approved