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%I #19 Sep 14 2022 21:11:37
%S 66,222,555,777,2222,3333,5555,7777,22222,33333,55555,77777,2222222,
%T 3333333,5555555,7777777,22222222222,33333333333,55555555555,
%U 77777777777,1111111111111,22222222222222222,33333333333333333,55555555555555555,77777777777777777,6666666666666666666
%N Sphenic numbers having identical digits.
%C Subsequence of A007304 (sphenic numbers: products of 3 distinct primes).
%C a(1)= A087331(4).
%H Max Alekseyev, <a href="/A268582/b268582.txt">Table of n, a(n) for n = 1..89</a>
%e 222 is in the sequence because 222 = 2*3*37, product of 3 distinct primes.
%p with(numtheory):
%p for n from 1 to 23 do:
%p for b from 1 to 9 do:
%p x:=(((10^n)- 1)/9)*b:y:=factorset(x):n1:=nops(y):
%p if bigomega(x)=3 and n1=3
%p then
%p printf(`%d, `,x):
%p else
%p fi:
%p od:
%p od:
%t 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 *)
%Y Cf. A007304, A046053, A087331, A095370, A196104.
%K nonn,base
%O 1,1
%A _Michel Lagneau_, Feb 07 2016
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