OFFSET
1,2
COMMENTS
For n > 9 the structure of digits represents the pyramids of Giza. Also the top of a mountain. The first digit is equal to the last digit. The first digits are in consecutive increasing order. The last digits are in consecutive decreasing order. The largest digit is the central digit. The number of digits is odd. This sequence has 45 terms. The final term is 12345678987654321. Giza numbers are mountain numbers A134941 and palindromes A002113.
There are 10 - k numbers with 2*k - 1 digits. - Omar E. Pol, Aug 04 2011
LINKS
Nathaniel Johnston, Table of n, a(n) for n = 1..45 (full sequence)
EXAMPLE
Illustration using the final term of this sequence:
. . . . . . . . 9 . . . . . . . .
. . . . . . . 8 . 8 . . . . . . .
. . . . . . 7 . . . 7 . . . . . .
. . . . . 6 . . . . . 6 . . . . .
. . . . 5 . . . . . . . 5 . . . .
. . . 4 . . . . . . . . . 4 . . .
. . 3 . . . . . . . . . . . 3 . .
. 2 . . . . . . . . . . . . . 2 .
1 . . . . . . . . . . . . . . . 1
PROG
(Python)
ups = [tuple(range(i, j)) for i in range(1, 10) for j in range(i+1, 11)]
afull = sorted(int("".join(map(str, u[:-1] + u[::-1]))) for u in ups)
print(afull) # Michael S. Branicky, Aug 02 2022
CROSSREFS
KEYWORD
easy,fini,full,nonn,base
AUTHOR
Omar E. Pol, Nov 25 2007, Nov 26 2007
STATUS
approved