

A182301


Composite numbers that are not perfect powers and whose prime factors have an equal number of digits in decimal representation.


2



6, 10, 12, 14, 15, 18, 20, 21, 24, 28, 30, 35, 40, 42, 45, 48, 50, 54, 56, 60, 63, 70, 72, 75, 80, 84, 90, 96, 98, 105, 108, 112, 120, 126, 135, 140, 143, 147, 150, 160, 162, 168, 175, 180, 187, 189, 192, 200, 209, 210, 221, 224, 240, 245, 247, 250, 252, 253, 270
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OFFSET

1,1


LINKS



EXAMPLE

30 = 2*3*5 belongs to this sequence, since its prime factors all have one digit and 30 is not a perfect power.


MATHEMATICA

lst1 = {}; lst2 = {}; r = 270; Do[b = IntegerDigits[FactorInteger[n]]; If[! PrimeQ[n] && Length[b[[1, 1]]] == Length[b[[1, 1]]], AppendTo[lst1, n]], {n, 4, r}]; lst2 = Complement[lst1, Union[Flatten[Table[n^i, {i, 2, Log[2, r]}, {n, 2, r^(1/i)}]]]]; lst2


CROSSREFS



KEYWORD

base,nonn


AUTHOR



STATUS

approved



