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!)
A209799 Composite numbers n such that the concatenation of the digits of the prime divisors of n is a prime number. 3
4, 6, 8, 9, 12, 16, 18, 21, 22, 24, 25, 27, 32, 33, 36, 39, 44, 46, 48, 49, 51, 54, 58, 63, 64, 66, 70, 72, 81, 82, 88, 92, 93, 96, 99, 108, 111, 115, 116, 117, 121, 125, 128, 132, 133, 140, 141, 142, 144, 147, 153, 154, 159, 162, 164, 165, 166, 169, 176, 177 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

70 is in the sequence because the prime divisors of 70 are {2,5,7} and 257 is prime.

MAPLE

read("transforms") ;

isA209799 := proc(n)

    local pdivs ;

    if isprime(n) or n < 4 then

        return false;

    end if;

    pdivs := sort(convert(numtheory[factorset](n), list)) ;

    isprime(digcatL(pdivs)) ;

end proc:

for n from 4 to 200 do

        if isA209799(n) then printf("%d, ", n) ;

        end if;

end do: # R. J. Mathar, Mar 19 2012

CROSSREFS

Cf. A000040, A084317, A084318.

Sequence in context: A079142 A062002 A090419 * A028958 A200878 A344030

Adjacent sequences:  A209796 A209797 A209798 * A209800 A209801 A209802

KEYWORD

nonn,base,less

AUTHOR

Michel Lagneau, Mar 13 2012

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 September 29 10:30 EDT 2022. Contains 357088 sequences. (Running on oeis4.)