A284294 Numbers using only digits 1 and 9.

1, 9, 11, 19, 91, 99, 111, 119, 191, 199, 911, 919, 991, 999, 1111, 1119, 1191, 1199, 1911, 1919, 1991, 1999, 9111, 9119, 9191, 9199, 9911, 9919, 9991, 9999, 11111, 11119, 11191, 11199, 11911, 11919, 11991, 11999, 19111, 19119, 19191, 19199, 19911, 19919

Offset

1,2

Comments

Product of digits of n is a power of 9; subsequence of A284295.

Prime terms are in A020457.

Links

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

Formula

The sum of first 2^n terms is (5*20^n + 38*10^n - 95*2^n + 1420)/171. Giovanni Resta, Mar 25 2017

Mathematica

Join @@ (FromDigits /@ Tuples[{1, 9}, #] & /@ Range[5]) (* Giovanni Resta, Mar 25 2017 *)

Prog

(Magma) [n: n in [1..20000] | Set(IntegerToSequence(n, 10)) subset {1, 9}]

Crossrefs

Cf. Numbers using only digits 1 and k for k = 0 and k = 2 - 9: A007088 (k = 0), A007931 (k = 2), A032917 (k = 3), A032822 (k = 4) , A276037 (k = 5), A284293 (k = 6), A276039 (k = 7), A213084 (k = 8), this sequence (k = 9).

Sequence in context: A329279 A372242 A284295 * A195572 A046259 A258452

Adjacent sequences: A284291 A284292 A284293 * A284295 A284296 A284297

Keyword

nonn,base

Author

Jaroslav Krizek, Mar 25 2017

Status

approved