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!)
A307764 Numbers m whose distinct prime factors are exactly the same as the distinct prime factors of each of the numbers obtained by deleting any single digit in the decimal expansion of m. 0
2500, 3600, 9600, 25000, 36000, 96000, 250000, 360000, 960000, 2500000, 3600000, 9600000, 25000000, 36000000, 96000000, 250000000, 360000000, 960000000, 2500000000, 3600000000, 9600000000, 25000000000, 36000000000, 96000000000, 250000000000, 360000000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: a(3n-2) = 25*10^(n+1), a(3n-1) = 36*10^(n+1) and a(3n) = 96*10^(n+1).

LINKS

Table of n, a(n) for n=1..26.

EXAMPLE

3600 is in the sequence because 3600, 360, 600 and 300 contain all the same prime factors 2, 3 and 5.

MAPLE

with(numtheory):nn:=10^10:

for n from 100 to nn do:

it:=0:x:=convert(n, base, 10):n0:=nops(x):d:=factorset(n):

W:=array(1..n0-1):

  for i from 1 to n0 do :

   k:=0:

   for j from n0 by -1 to 1 do:

    if j<>i

     then

     k:=k+1: W[k]:=x[j]:

     else

    fi:

   od:

    s:=sum(ā€˜W[i]*10^(n0-i-1)ā€™, ā€˜iā€™=1..n0-1):d1:=factorset(s):

      if d=d1

       then

       it:=it+1:

       else

      fi:

   od:

    if it=n0

     then

     printf(`%d, `, n):

     else

    fi:

od:

MATHEMATICA

rad[0] = 0; rad[n_] := Times @@ (First@# & /@ FactorInteger[n]); Select[Range[ 10^6], {rad[#]} == Union[rad /@ (FromDigits/@Subsets[(d = IntegerDigits[#]), {Length[d] - 1}])] &] (* Amiram Eldar, Jul 26 2019 *)

CROSSREFS

Cf. A027748.

Sequence in context: A248548 A252315 A131523 * A062120 A220025 A253377

Adjacent sequences:  A307761 A307762 A307763 * A307765 A307766 A307767

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Jul 24 2019

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 May 9 13:42 EDT 2021. Contains 343742 sequences. (Running on oeis4.)