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%I #11 Jun 06 2020 16:53:00
%S 0,1,10,11,100,101,110,111,1000,1001,10,11,110,111,1100,1101,1110,
%T 1111,11000,11001,100,101,1010,1011,10100,10101,10110,10111,101000,
%U 101001,110,111,1110,1111,11100,11101,11110,11111,111000,111001,1000,1001,10010,10011
%N In decimal representation of n: replace each digit with its binary representation.
%C a(n) = n iff (largest digit of n) = 1: a(A007088(n)) = A007088(n);
%C a(n) = A007088(A080719(n)).
%H Reinhard Zumkeller, <a href="/A257831/b257831.txt">Table of n, a(n) for n = 0..10000</a>
%e . n | dec --> bin | a(n) | A080719(n)
%e . -----+--------------------------+----------+------------
%e . 100 | [1,0,0] | [1,0,0] | 100 | 4
%e . 101 | [1,0,1] | [1,0,1] | 101 | 5
%e . 102 | [1,0,2] | [1,0,10] | 1010 | 10
%e . 103 | [1,0,3] | [1,0,11] | 1011 | 11
%e . 104 | [1,0,4] | [1,0,100] | 10100 | 20
%e . 105 | [1,0,5] | [1,0,101] | 10101 | 21
%e . 106 | [1,0,6] | [1,0,110] | 10110 | 22
%e . 107 | [1,0,7] | [1,0,111] | 10111 | 23
%e . 108 | [1,0,8] | [1,0,1000] | 101000 | 40
%e . 109 | [1,0,9] | [1,0,1001] | 101001 | 41
%e . 110 | [1,1,0] | [1,1,0] | 110 | 6
%e . 111 | [1,1,1] | [1,1,1] | 111 | 7
%e . 112 | [1,1,2] | [1,1,10] | 1110 | 14
%e . 113 | [1,1,3] | [1,1,11] | 1111 | 15
%e . 114 | [1,1,4] | [1,1,100] | 11100 | 28
%e . 115 | [1,1,5] | [1,1,101] | 11101 | 29
%e . 116 | [1,1,6] | [1,1,110] | 11110 | 30
%e . 117 | [1,1,7] | [1,1,111] | 11111 | 31
%e . 118 | [1,1,8] | [1,1,1000] | 111000 | 56
%e . 119 | [1,1,9] | [1,1,1001] | 111001 | 57
%e . 120 | [1,2,0] | [1,10,0] | 1100 | 12
%e . 121 | [1,2,1] | [1,10,1] | 1101 | 13
%e . 122 | [1,2,2] | [1,10,10] | 11010 | 26
%e . 123 | [1,2,3] | [1,10,11] | 11011 | 27
%e . 124 | [1,2,4] | [1,10,100] | 110100 | 52
%e . 125 | [1,2,5] | [1,10,101] | 110101 | 53 .
%t Table[FromDigits[Flatten[IntegerDigits[#,2]&/@IntegerDigits[n]]],{n,0,50}] (* _Harvey P. Dale_, Jun 06 2020 *)
%o (Haskell)
%o import Data.Maybe (mapMaybe)
%o a257831 = foldr (\b v -> 10 * v + b) 0 .
%o concat . mapMaybe (flip lookup bin) . a031298_row
%o where bin = zip [0..9] a030308_tabf
%o (Python)
%o def A257831(n):
%o ....return int(''.join((format(int(d),'b') for d in str(n))))
%o # _Chai Wah Wu_, May 10 2015
%Y Cf. A007088, A030308, A031298, A080719.
%K nonn,base
%O 0,3
%A _Reinhard Zumkeller_, May 10 2015
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