cp's OEIS Frontend

A266139 Volcano palindromes: palindromes not in A110784 such that removing one digit will result in a term in A110784.

%I A266139 #12 Aug 22 2021 00:15:46
%S A266139 0,1,2,3,4,5,6,7,8,9,101,202,212,303,313,323,404,414,424,434,505,515,
%T A266139 525,535,545,606,616,626,636,646,656,707,717,727,737,747,757,767,808,
%U A266139 818,828,838,848,858,868,878,909,919,929,939,949,959,969,979,989,11011
%N A266139 Volcano palindromes: palindromes not in A110784 such that removing one digit will result in a term in A110784.
%C A266139 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.
%C A266139 Illustration using a term of this sequence, 23446564432:
%C A266139 .  .  .  .  6  .  6  .  .  .  .
%C A266139 .  .  .  .  .  5  .  .  .  .  .
%C A266139 .  .  4  4  .  .  .  4  4  .  .
%C A266139 .  3  .  .  .  .  .  .  .  3  .
%C A266139 2  .  .  .  .  .  .  .  .  .  2
%H A266139 Chai Wah Wu, <a href="/A266139/b266139.txt">Table of n, a(n) for n = 1..10000</a>
%o A266139 (Python)
%o A266139 from itertools import combinations_with_replacement as mc
%o A266139 def agentod(digits):
%o A266139     yield from range(10)
%o A266139     for d in range(3, digits+1, 2):
%o A266139         for left in mc("123456789", d//2):
%o A266139             for center in range(int(left[-1])):
%o A266139                 yield int("".join(left + (str(center), ) + left[::-1]))
%o A266139 print([an for an in agentod(5)]) # _Michael S. Branicky_, Aug 21 2021
%Y A266139 Cf. A110784.
%K A266139 nonn,easy,base
%O A266139 1,3
%A A266139 _Chai Wah Wu_, Dec 25 2015