A347400 - OEIS

%I #7 Aug 30 2021 21:48:43

%S 1,2,3,4,5,6,7,8,9,101,11,21,31,41,51,61,71,81,91,102,12,22,32,42,52,

%T 62,72,82,92,103,13,23,33,43,53,63,73,83,93,104,14,24,34,44,54,64,74,

%U 84,94,105,15,25,35,45,55,65,75,85,95,106,16,26,36,46,56,66,76,86,96,107,17,27,37,47,57

%N Lexicographically earliest sequence of distinct terms > 0 such that concatenating n to a(n) forms a palindrome in base 10.

%e For n = 8 we have a(8) = 8 and 88 is a palindrome in base 10;

%e for n = 9 we have a(9) = 9 and 99 is a palindrome in base 10;

%e for n = 10 we have a(10) = 101 and 10101 is a palindrome in base 10;

%e for n = 11 we have a(11) = 11 and 1111 is a palindrome in base 10;

%e for n = 12 we have a(12) = 21 and 1221 is a palindrome in base 10; etc.

%o (Python)

%o def ispal(s): return s == s[::-1]

%o def aupton(terms):

%o     alst, seen = [1], {1}

%o     for n in range(2, terms+1):

%o         an = 1

%o         while an in seen or not ispal(str(n) + str(an)): an += 1

%o         alst.append(an); seen.add(an)

%o     return alst

%o print(aupton(200)) # _Michael S. Branicky_, Aug 30 2021

%Y Cf. A347335, A347336, A347401, A347402.

%K base,nonn

%O 1,2

%A _Eric Angelini_ and _Carole Dubois_, Aug 30 2021