OFFSET
1,1
COMMENTS
The structure of digits represents an acute angle. The vertex is an internal digit. In the graphic representation the points are connected by imaginary line segments from left to right. This sequence is finite. The final term has 14 digits: 98765432102468.
LINKS
Micah Manary, Table of n, a(n) for n = 1..2337
Micah Manary, Python program
FORMULA
If a(n) does not end in 0, then A004086(a(n)) is a term; if a(n) does not start with 9, then A061601(a(n)) is a term. - Michael S. Branicky, Aug 02 2022
EXAMPLE
Illustration using the final term of this sequence:
9 . . . . . . . . . . . . .
. 8 . . . . . . . . . . . 8
. . 7 . . . . . . . . . . .
. . . 6 . . . . . . . . 6 .
. . . . 5 . . . . . . . . .
. . . . . 4 . . . . . 4 . .
. . . . . . 3 . . . . . . .
. . . . . . . 2 . . 2 . . .
. . . . . . . . 1 . . . . .
. . . . . . . . . 0 . . . .
PROG
(Python)
progressions = set(tuple(range(i, j+1, d)) for i in range(10) for d in range(1, 10-i) for j in range(i+d, 10))
s = set()
for left in progressions:
for right in progressions:
dl, dr = left[1] - left[0], right[1] - right[0]
if dl + dr > 2:
if left[-1] == right[-1]: s.add(left[:-1] + right[::-1])
if left[0] == right[0]: s.add(left[::-1] + right[1:])
afull = sorted(int("".join(map(str, t))) for t in s if t[0] != 0)
print(afull[:53]) # Michael S. Branicky, Aug 02 2022
CROSSREFS
KEYWORD
base,fini,nonn,full
AUTHOR
Omar E. Pol, Dec 02 2007
STATUS
approved