login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A143967 Numbers containing only digits 3 or 7 in decimal representation. 6
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 17 14:39 EDT 2019. Contains 325106 sequences. (Running on oeis4.)