A284964 Numbers with digits 3 and 9 only.

3, 9, 33, 39, 93, 99, 333, 339, 393, 399, 933, 939, 993, 999, 3333, 3339, 3393, 3399, 3933, 3939, 3993, 3999, 9333, 9339, 9393, 9399, 9933, 9939, 9993, 9999, 33333, 33339, 33393, 33399, 33933, 33939, 33993, 33999, 39333, 39339, 39393, 39399, 39933, 39939

Offset: 1

Author

Jaroslav Krizek, Apr 06 2017

Keywords

• nonn
• base

Comments

All terms > 3 are composite.

Crossrefs

Cf. Numbers with digits 3 and k only for k = 0 - 2 and 4 - 9: A169966 (k = 0), A032917 (k = 1), A032810 (k = 2), A032834 (k = 4), A284379 (k = 5), A284633 (k = 6), A143967 (k = 7), A284963 (k = 8), this sequence (k = 9).

Programs

Magma

[n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {3, 9}]

Mathematica

Table[FromDigits/@Tuples[{3,9},n],{n,5}]//Flatten (* Harvey P. Dale, Sep 20 2022 *)

Formula

a(n) = 3 * A032917(n).