OFFSET
1,3
LINKS
Rémy Sigrist, Table of n, a(n) for n = 1..10000
Rémy Sigrist, PARI program
EXAMPLE
a(7)=5 because we reach 5 terms starting from the most recent term a(6) (each line shows the next unvisited term(s) we can reach from the term(s) in the previous iteration):
1, 1, 2, 3, 4, 4
1<----------4
1, 1, 2, 3, 4, 4
1<-1->2
1, 1, 2, 3, 4, 4
2---->4
From the last iteration we can visit no new terms. We reached 5 terms, so a(7)=5:
1, 1, 2, 3, 4, 4
1 1 2 4 4
PROG
(Python)
def A(lastn, mode=0):
a, n, t=[1], 0, 1
while n<lastn:
d, g, r, rr=[[n]], 0, 0, [n]
while len(d)>0:
if not d[-1][-1] in rr:rr.append(d[-1][-1])
if d[-1][-1]-a[d[-1][-1]]>=0:
if d[-1].count(d[-1][-1]-a[d[-1][-1]])<t:g=1
if d[-1][-1]+a[d[-1][-1]]<=n:
if d[-1].count(d[-1][-1]+a[d[-1][-1]])<t:
if g>0: d.append(d[-1][:])
d[-1].append(d[-1][-1]+a[d[-1][-1]])
r=1
if g>0:
if r>0: d[-2].append(d[-2][-1]-a[d[-2][-1]])
else: d[-1].append(d[-1][-1]-a[d[-1][-1]])
r=1
if r==0:d.pop()
r, g=0, 0
a.append(len(rr))
n+=1
print(n+1, a[n])
if mode>0: print(a)
return a # S. Brunner, Feb 26 2023
(PARI) See Links section.
CROSSREFS
KEYWORD
nonn
AUTHOR
Neal Gersh Tolunsky, Feb 18 2023
STATUS
approved