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A023745
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Digits in base 3 are in nondecreasing order.
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5
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0, 1, 2, 4, 5, 8, 13, 14, 17, 26, 40, 41, 44, 53, 80, 121, 122, 125, 134, 161, 242, 364, 365, 368, 377, 404, 485, 728, 1093, 1094, 1097, 1106, 1133, 1214, 1457, 2186, 3280, 3281, 3284, 3293, 3320, 3401, 3644, 4373, 6560, 9841, 9842, 9845, 9854
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| Harvey P. Dale, Table of n, a(n) for n = 0..1000
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FORMULA
| Numbers that in ternary are the concatenation of i 1's with j 2's, i, j>=0. Also a(n) = A073216(n+1) - 1. Proof: Write a(n) as 1{m}2{n}, then adding 1 gives 1{m-1}20{n} for m>0 and 10{n} for m=0. Doubling yields 10{m-1}10{n} or 20{n}, respectively. These two forms exactly describe the forms of sums of two powers of 3, the two powers being 3^n and 3^(m+n). - Hugo van der Sanden.
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MATHEMATICA
| Select[Range[0, 10000], !Negative[Min[Differences[IntegerDigits[ #, 3]]]]&] (* or *) With[{nn=10}, FromDigits[#, 3]&/@Union[Flatten[Table[ PadRight[ PadLeft[{}, n, 1], x, 2], {n, 0, nn}, {x, 0, nn}], 1]]] (* From Harvey P. Dale, Oct 12 2011 *)
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CROSSREFS
| Sequence in context: A116901 A102829 A031988 * A178656 A085443 A164571
Adjacent sequences: A023742 A023743 A023744 * A023746 A023747 A023748
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KEYWORD
| nonn,base,easy
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AUTHOR
| Olivier Gerard (olivier.gerard(AT)gmail.com)
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