A143967 Numbers containing only digits 3 or 7 in decimal representation.

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

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