login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A079651 Prime numbers using only the straight digits 1, 4 and 7. 8
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
The smallest prime using only all three straight digits is a(9) = 1447 (see Prime Curios! link). - Bernard Schott, Sep 08 2023
LINKS
Chris K. Caldwell and G. L. Honaker, Jr., 1447, Prime Curios! [Gupta]
EXAMPLE
17 is a term 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
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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 21 01:13 EDT 2024. Contains 373535 sequences. (Running on oeis4.)