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 A284294 Numbers using only digits 1 and 9. 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Product of digits of n is a power of 9; subsequence of A284295. Prime terms are in A020457. LINKS 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: A090771 A329279 A284295 * A195572 A046259 A258452 Adjacent sequences:  A284291 A284292 A284293 * A284295 A284296 A284297 KEYWORD nonn,base AUTHOR Jaroslav Krizek, Mar 25 2017 STATUS approved

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Last modified February 27 06:36 EST 2020. Contains 332299 sequences. (Running on oeis4.)