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A284636
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Numbers with digits 6 and 9 only.
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5
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6, 9, 66, 69, 96, 99, 666, 669, 696, 699, 966, 969, 996, 999, 6666, 6669, 6696, 6699, 6966, 6969, 6996, 6999, 9666, 9669, 9696, 9699, 9966, 9969, 9996, 9999, 66666, 66669, 66696, 66699, 66966, 66969, 66996, 66999, 69666, 69669, 69696, 69699, 69966, 69969
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refs;
listen;
history;
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internal format)
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OFFSET
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1,1
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COMMENTS
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All terms are composite.
All terms are divisible by 3. - Michael S. Branicky, Jun 09 2021
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LINKS
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Felix Fröhlich, Table of n, a(n) for n = 1..10000
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FORMULA
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a(n) = 3 * A032810(n).
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MATHEMATICA
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Table[FromDigits /@ Tuples[{6, 9}, n], {n, 5}] // Flatten (* or *)
Select[Range@ 70000, Total@ Pick[DigitCount@ #, {0, 0, 0, 0, 0, 1, 0, 0, 1, 0}, 0] == 0 &] (* Michael De Vlieger, Apr 02 2017 *)
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PROG
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(Magma) [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {6, 9}]
(PARI)
a(n) = {
my(z, e = logint(n+1, 2, &z),
t1 = 9 * subst(Pol(binary(n+1-z), 'x), 'x, 10),
t2 = 6 * subst(Pol(binary(2*z-2-n), 'x), 'x, 10));
t1+t2;
};
vector(44, n, a(n)) \\ Gheorghe Coserea, Apr 04 2017
(Python)
def a(n): return int(bin(n+1)[3:].replace('0', '6').replace('1', '9'))
print([a(n) for n in range(1, 45)]) # Michael S. Branicky, Jun 09 2021
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CROSSREFS
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Cf. A032810.
Numbers n with digits 6 and k only for k = 0 - 5 and 7 - 9: A204093 (k = 0), A284293 (k = 1), A284632 (k = 2), A284633 (k = 3), A284634 (k = 4), A256291 (k = 5), A256292 (k = 7), A284635 (k = 8), this sequence (k = 9).
Sequence in context: A061401 A359800 A264380 * A046498 A119738 A299917
Adjacent sequences: A284633 A284634 A284635 * A284637 A284638 A284639
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KEYWORD
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nonn,base
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AUTHOR
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Jaroslav Krizek, Apr 02 2017
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STATUS
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approved
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