login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A079651 Prime numbers using only the straight digits 1, 4 and 7. 7
7, 11, 17, 41, 47, 71, 1117, 1171, 1447, 1471, 1741, 1747, 1777, 4111, 4177, 4441, 4447, 7177, 7411, 7417, 7477, 7717, 7741, 11117, 11171, 11177, 11411, 11447, 11471, 11717, 11777, 14177, 14411, 14447, 14717, 14741, 14747, 14771, 17117, 17417 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The number of decimal digits of a(n) is never divisible by 3. - Robert Israel, May 22 2014

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

17 is in the sequence because it is a prime and consists of straight digits 1 and 7 only.

MAPLE

f:= proc(x) local n, d, t, i, a;

n:= floor(log[3]((2*x+3)));

if n mod 3 = 0 then return 0 fi;

d:=x - (3^n - 3)/2;

t:= 0;

for i from 0 to n-1 do

   a:= d mod 3;

   t:= t + (3*a+1)*10^i;

   d:= (d-a)/3;

od:

t

end proc:

select(isprime, map(f, [$1..1000])); # Robert Israel, May 22 2014

MATHEMATICA

Select[Prime[Range[2000]], Union[ Join[ IntegerDigits[ # ], {1, 4, 7}]] == {1, 4, 7} &]

PROG

(PARI) straight(n)=my(t); while(n, t=n%10; if(t!=1&&t!=4&&t!=7, return(0)); n\=10); !!t

select(straight, primes(1000)) \\ Charles R Greathouse IV, Sep 25 2012

CROSSREFS

Cf. A028373.

Sequence in context: A158594 A215419 A107642 * A178386 A097956 A094104

Adjacent sequences:  A079648 A079649 A079650 * A079652 A079653 A079654

KEYWORD

base,nonn

AUTHOR

Shyam Sunder Gupta, Jan 23 2003

EXTENSIONS

Corrected and extended by Robert G. Wilson v, Jan 24 2003

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 September 29 14:39 EDT 2020. Contains 337432 sequences. (Running on oeis4.)