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Search: id:A061915
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| A061915 |
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Obtain m by omitting trailing zeros from n; a(n) = smallest multiple k*m which is a palindrome with even digits, or -1 if no such multiple exists. |
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+0
4
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| 0, 2, 2, 6, 4, -1, 6, 686, 8, 666, 2, 22, 444, 2002, 686, -1, 464, 646, 666, 646, 2, 6006, 22, 828, 888, -1, 2002, 8886888, 868, 464, 6, 868, 4224, 66, 646, -1, 828, 222, 646, 6006, 4, 22222, 6006, 68886, 44, -1, 828, 282, 4224, 686, -1, 42024, 4004, 424, 8886888, -1, 8008, 68286, 464, 68086, 6
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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a(n) = -1 if and only if m ends with the digit 5.
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LINKS
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P. De Geest, Smallest multipliers to make a number palindromic.
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EXAMPLE
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For n = 30 we have m = 3; 3*2 = 6 is a palindrome with even digits, so a(30) = 6.
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PROGRAM
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(ARIBAS): stop := 500000; for n := 0 to 60 do k := 1; test := true; while test and k < stop do mp := omit_trailzeros(n)*k; if test := not all_even(mp) or mp <> int_reverse(mp) then inc(k); end; end; if k < stop then write(mp, " "); else write(-1, " "); end; end;
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CROSSREFS
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Cf. A050782, A062293, A061816, A061906. Values of k are given in A061916.
Sequence in context: A130712 A130728 A092384 this_sequence A138565 A137316 A064851
Adjacent sequences: A061912 A061913 A061914 this_sequence A061916 A061917 A061918
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KEYWORD
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base,sign,easy
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AUTHOR
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Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Jun 25 2001
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