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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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Arkadiusz Wesolowski, Table of n, a(n) for n = 1..10000
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
Subsequence of A199009.
Sequence in context: A296205 A325281 A100658 * A069059 A273157 A139587
KEYWORD
base,nonn
AUTHOR
STATUS
approved

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Last modified May 24 05:24 EDT 2024. Contains 372772 sequences. (Running on oeis4.)