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A348099
Starts of runs of 3 consecutive numbers that have an equal number of unitary and nonunitary prime divisors (A348097).
3
423, 603, 1250, 1375, 2007, 2523, 2527, 3175, 4075, 4203, 4374, 4923, 4948, 7442, 8991, 10375, 10467, 12591, 18027, 20402, 20575, 22023, 22687, 23823, 26071, 28375, 30231, 31507, 31850, 33271, 34623, 35574, 36162, 37348, 40023, 49975, 50274, 54475, 54511, 55323
OFFSET
1,1
LINKS
FORMULA
423 is a term since 423 = 3^2 * 47, 423 + 1 = 424 = 2^3 * 53 and 423 + 2 = 425 = 5^2 * 17 all have one unitary prime divisor and one nonunitary prime divisor.
MATHEMATICA
q[n_] := n == 1 || Count[(e = FactorInteger[n][[;; , 2]]), 1] == Length[e]/2; v = q /@ Range[3]; seq = {}; Do[v = Append[Drop[v, 1], q[k]]; If[And @@ v, AppendTo[seq, k - 2]], {k, 4, 10^5}]; seq
CROSSREFS
Subsequence of A348097 and A348098.
Cf. A335397.
Sequence in context: A231939 A203099 A365865 * A096024 A205980 A206662
KEYWORD
nonn
AUTHOR
Amiram Eldar, Sep 30 2021
STATUS
approved