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A004186
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Arrange digits of n in decreasing order.
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32
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 21, 31, 41, 51, 61, 71, 81, 91, 20, 21, 22, 32, 42, 52, 62, 72, 82, 92, 30, 31, 32, 33, 43, 53, 63, 73, 83, 93, 40, 41, 42, 43, 44, 54, 64, 74, 84, 94, 50, 51, 52, 53, 54, 55, 65, 75, 85, 95, 60, 61, 62, 63, 64, 65, 66, 76, 86, 96, 70, 71, 72
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,3
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COMMENTS
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a(A009996(n)) = A009996(n). - Reinhard Zumkeller, Oct 31 2007
If we define "sortable primes" as prime numbers that remain prime when their digits are sorted in decreasing order, then all absolute primes (A003459) are sortable primes but not all sortable primes are absolute primes. For example, 113 is both sortable and absolute, and 313 is sortable but not absolute since its digits can be permuted to 133 = 7 * 19. - Alonso del Arte, Oct 05 2013
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LINKS
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R. Zumkeller, Table of n, a(n) for n = 0..10000
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EXAMPLE
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a(19) = 91 because the digits of 19 being 1 and 9, arranged in decreasing order they are 9 and 1.
a(20) = 20 because the digits are already in decreasing order.
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MAPLE
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A004186 := proc(n)
local dgs;
convert(n, base, 10) ;
dgs := sort(%) ;
add( op(i, dgs)*10^(i-1), i=1..nops(dgs)) ;
end proc:
seq(A004186(n), n=0..20) ; # R. J. Mathar, Jul 26 2015
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MATHEMATICA
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sortDigitsDown[n_] := FromDigits@ Reverse@ Sort@ IntegerDigits@ n; Array[sortDigitsDown, 73, 0] (* Robert G. Wilson v, Aug 19 2011 *)
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PROG
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(PARI)
reconstruct(m) = {local(r); r=0; for(i=1, matsize(m)[2], r=r*10+m[i]); r}
A004186(n) = reconstruct(vecsort(digits(n), , 4))
\\ Michael B. Porter, Nov 11 2009
(PARI) a(n) = fromdigits(vecsort(digits(n), , 4)); \\ Joerg Arndt, Feb 24 2019
(Haskell)
import Data.List (sort)
a004186 = read . reverse . sort . show :: Integer -> Integer
-- Reinhard Zumkeller, Aug 19 2011
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CROSSREFS
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Cf. A004185, A004086, A009996, A064222, A194233, A032553, A032554, A028907, A028908.
Sequence in context: A321474 A225805 A068637 * A034704 A276512 A023792
Adjacent sequences: A004183 A004184 A004185 * A004187 A004188 A004189
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KEYWORD
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nonn,base,look
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AUTHOR
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N. J. A. Sloane.
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EXTENSIONS
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More terms from Reinhard Zumkeller, Oct 31 2007
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STATUS
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approved
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