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 A143967 Numbers containing only digits 3 or 7 in decimal representation. 7
 3, 7, 33, 37, 73, 77, 333, 337, 373, 377, 733, 737, 773, 777, 3333, 3337, 3373, 3377, 3733, 3737, 3773, 3777, 7333, 7337, 7373, 7377, 7733, 7737, 7773, 7777, 33333, 33337, 33373, 33377, 33733, 33737, 33773, 33777, 37333, 37337, 37373, 37377 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS See A020463 for primes. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA a(n) = f(n+1, 0) with f(n, x) = if n=1 then A004086(x) else f(floor(n/2), 10*x + 3 + 4*(n mod 2)). MATHEMATICA Table[FromDigits/@Tuples[{3, 7}, n], {n, 5}]//Flatten (* Harvey P. Dale, Aug 28 2017 *) PROG (Haskell) a143967 = f 0 . (+ 1) where f y 1 = a004086 y f y x = f (10 * y + 3 + 4 * r) x' where (x', r) = divMod x 2 -- Reinhard Zumkeller, Mar 18 2015 CROSSREFS Cf. A004086, A020463, A032810. Sequence in context: A115088 A089622 A241147 * A007646 A238314 A120566 Adjacent sequences: A143964 A143965 A143966 * A143968 A143969 A143970 KEYWORD base,nonn AUTHOR Reinhard Zumkeller, Sep 06 2008 STATUS approved

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Last modified August 6 15:42 EDT 2024. Contains 374974 sequences. (Running on oeis4.)