A047813 Largest palindromic substring of n.
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 11, 2, 3, 4, 5, 6, 7, 8, 9, 2, 2, 22, 3, 4, 5, 6, 7, 8, 9, 3, 3, 3, 33, 4, 5, 6, 7, 8, 9, 4, 4, 4, 4, 44, 5, 6, 7, 8, 9, 5, 5, 5, 5, 5, 55, 6, 7, 8, 9, 6, 6, 6, 6, 6, 6, 66, 7, 8, 9, 7, 7, 7, 7, 7, 7, 7, 77, 8, 9, 8, 8, 8, 8, 8, 8, 8, 8, 88, 9, 9, 9, 9, 9, 9, 9
Offset: 0
Examples
a(1313) = Max{1,3,131,313} = 313.
Links
- Reinhard Zumkeller, Table of n, a(n) for n = 0..10000
- Index entries for sequences related to palindromes
Programs
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Haskell
a047813 = last . a262188_row -- Reinhard Zumkeller, Sep 14 2015, Aug 23 2011
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Mathematica
palQ[n_Integer, base_Integer] := Module[{idn = IntegerDigits[n, base]}, idn == Reverse[ idn]]; f[n_] := Block[{id = IntegerDigits@ n, mx = -Infinity}, k = Length@ id; While[k > 0 && mx == -Infinity, mx = Max[mx, Select[ FromDigits@# & /@ Partition[id, k, 1], palQ[#, 10] &]]; k--]; mx] (* Robert G. Wilson v, Aug 24 2011 *) lps[n_]:=Module[{idn=IntegerDigits[n]},Max[FromDigits/@Select[ Flatten[ Table[ Partition[ idn,i,1],{i,Length[idn]}],1],#==Reverse[#]&]]]; Array[ lps,100,0] (* Harvey P. Dale, Jan 09 2015 *) -
Python
def c(s): return (s[0] != "0" or s == "0") and s == s[::-1] def a(n): s = str(n) ss = (s[i:j] for i in range(len(s)) for j in range(i+1, len(s)+1)) return max(int(w) for w in ss if c(w)) print([a(n) for n in range(96)]) # Michael S. Branicky, Sep 18 2022
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