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A284636 Numbers with digits 6 and 9 only. 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are composite.

LINKS

Table of n, a(n) for n=1..44.

FORMULA

a(n) = 3 * A032810(n).

MATHEMATICA

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 *)

PROG

(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

CROSSREFS

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: A056416 A061401 A264380 * A046498 A119738 A299917

Adjacent sequences:  A284633 A284634 A284635 * A284637 A284638 A284639

KEYWORD

nonn,base

AUTHOR

Jaroslav Krizek, Apr 02 2017

STATUS

approved

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Last modified July 5 00:01 EDT 2020. Contains 335457 sequences. (Running on oeis4.)