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A056524 Palindromes with even number of digits.

%I A056524 #43 Nov 02 2021 11:00:59
%S A056524 11,22,33,44,55,66,77,88,99,1001,1111,1221,1331,1441,1551,1661,1771,
%T A056524 1881,1991,2002,2112,2222,2332,2442,2552,2662,2772,2882,2992,3003,
%U A056524 3113,3223,3333,3443,3553,3663,3773,3883,3993,4004,4114,4224,4334,4444,4554
%N A056524 Palindromes with even number of digits.
%C A056524 Concatenation of n with reverse of n (keeping leading zeros in the reverse).
%C A056524 A178788(a(n)) = 0 for n > 1. - _Reinhard Zumkeller_, Jun 30 2010
%C A056524 All of the terms are divisible by eleven. - _James Burling_, Aug 08 2014
%H A056524 Reinhard Zumkeller, <a href="/A056524/b056524.txt">Table of n, a(n) for n = 1..9999</a>
%F A056524 a(n) = n*10^A055642(n) + A004086(n).
%F A056524 a(n) = 11 * A066492(n).
%t A056524 d[n_]:=IntegerDigits[n]; Table[FromDigits[Join[x=d[n],Reverse[x]]],{n,45}] (* _Jayanta Basu_, May 29 2013 *)
%t A056524 Select[Flatten[Table[Range[10^n,10^(n+1)-1],{n,1,3,2}]],PalindromeQ] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Feb 22 2018 *)
%o A056524 (Haskell)
%o A056524 a056524 n = a056524_list !! (n-1)
%o A056524 a056524_list = [read (ns ++ reverse ns) :: Integer |
%o A056524                 n <- [0..], let ns = show n]
%o A056524 -- _Reinhard Zumkeller_, Dec 28 2011
%o A056524 (Python)
%o A056524 def a(n): s = str(n); return int(s + s[::-1])
%o A056524 print([a(n) for n in range(1, 46)]) # _Michael S. Branicky_, Nov 02 2021
%Y A056524 Cf. A002113, A004086, A056525, A066492.
%Y A056524 Cf. A020338, A055642, A178788.
%Y A056524 Cf. A110745 (permutation).
%K A056524 base,easy,nonn
%O A056524 1,1
%A A056524 _Henry Bottomley_, Jun 16 2000