OFFSET
0,3
COMMENTS
The definition of an orbital system is given in A232500 (see also the illustration there). The number of orbitals over n sectors is counted by the swinging factorial A056040.
An orbital w has a 'peak' at i+1 when signum(w[i]) < signum(w[i+1]) and signum(w[i+1]) > signum(w[i+2]).
A097692 is a subtriangle.
LINKS
Peter Luschny, Orbitals
EXAMPLE
Triangle read by rows, n>=0. The length of row n is floor((n+1)/2) for n>=1.
[ n] [k=0,1,2,...] [row sum]
[ 0] [ 1] 1
[ 1] [ 1] 1
[ 2] [ 2] 2
[ 3] [ 4, 2] 6
[ 4] [ 4, 2] 6
[ 5] [ 12, 15, 3] 30
[ 6] [ 10, 8, 2] 20
[ 7] [ 38, 68, 30, 4] 140
[ 8] [ 26, 30, 12, 2] 70
[ 9] [121, 272, 183, 49, 5] 630
[10] [ 70, 104, 60, 16, 2] 252
[11] [384, 1026, 912, 372, 72, 6] 2772
[12] [192, 350, 260, 100, 20, 2] 924
T(6, 2) = 2 because the two orbitals [-1, 1, -1, 1, -1, 1] and [1, -1, 1, -1, 1, -1] have 2 peaks.
PROG
(Sage) # uses[unit_orbitals from A274709]
# Brute force counting
def orbital_peaks(n):
if n == 0: return [1]
S = [0]*((n+1)//2)
for u in unit_orbitals(n):
L = [1 if sgn(u[i]) < sgn(u[i+1]) and sgn(u[i+1]) > sgn(u[i+2]) else 0 for i in (0..n-3)]
S[sum(L)] += 1
return S
for n in (0..12): print(orbital_peaks(n))
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
Peter Luschny, Jul 10 2016
STATUS
approved