

A266139


Volcano palindromes: palindromes not in A110784 such that removing one digit will result in a term in A110784.


2



0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 101, 202, 212, 303, 313, 323, 404, 414, 424, 434, 505, 515, 525, 535, 545, 606, 616, 626, 636, 646, 656, 707, 717, 727, 737, 747, 757, 767, 808, 818, 828, 838, 848, 858, 868, 878, 909, 919, 929, 939, 949, 959, 969, 979, 989, 11011
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OFFSET

1,3


COMMENTS

All terms have odd number of digits. Terms are palindromes such that digits are nondecreasing halfway through except for the middle digit, which is strictly smaller than its neighboring digits.
Illustration using a term of this sequence, 23446564432:
. . . . 6 . 6 . . . .
. . . . . 5 . . . . .
. . 4 4 . . . 4 4 . .
. 3 . . . . . . . 3 .
2 . . . . . . . . . 2


LINKS



PROG

(Python)
from itertools import combinations_with_replacement as mc
def agentod(digits):
yield from range(10)
for d in range(3, digits+1, 2):
for left in mc("123456789", d//2):
for center in range(int(left[1])):
yield int("".join(left + (str(center), ) + left[::1]))


CROSSREFS



KEYWORD

nonn,easy,base


AUTHOR



STATUS

approved



