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!)
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
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(‘W[i]*10^(n0-i-1)’, ‘i’=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
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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 29 07:00 EST 2024. Contains 370414 sequences. (Running on oeis4.)