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A268582 Sphenic numbers having identical digits. 0
66, 222, 555, 777, 2222, 3333, 5555, 7777, 22222, 33333, 55555, 77777, 2222222, 3333333, 5555555, 7777777, 22222222222, 33333333333, 55555555555, 77777777777, 1111111111111, 22222222222222222, 33333333333333333, 55555555555555555, 77777777777777777, 6666666666666666666 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A007304 (sphenic numbers: products of 3 distinct primes).

a(1)= A087331(4).

LINKS

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

EXAMPLE

222 is in the sequence because 222 = 2*3*37, product of 3 distinct primes.

MAPLE

with(numtheory):

for n from 1 to 23 do:

  for b from 1 to 9 do:

    x:=(((10^n)- 1)/9)*b:y:=factorset(x):n1:=nops(y):

     if bigomega(x)=3 and n1=3

      then

      printf(`%d, `, x):

      else

     fi:

   od:

od:

MATHEMATICA

Select[Flatten@ Map[Map[Function[k, FromDigits@ Table[k, {#}]], Range[1, 9]] &, Range@ 20], Length@ # == 3 && Times @@ Last /@ # == 1 &@ FactorInteger@ # &] (* Michael De Vlieger, Feb 07 2016 *)

CROSSREFS

Cf. A007304, A046053, A087331, A095370, A196104.

Sequence in context: A074873 A205817 A046393 * A117306 A322768 A158070

Adjacent sequences:  A268579 A268580 A268581 * A268583 A268584 A268585

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Feb 07 2016

STATUS

approved

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Last modified August 7 23:50 EDT 2022. Contains 355995 sequences. (Running on oeis4.)