A076251 Numbers m such that omega(m) = omega(m-1) + omega(m-2), where omega(m) is the number of distinct prime factors of m.
3, 6, 10, 18, 30, 33, 42, 60, 66, 84, 90, 102, 105, 110, 114, 126, 129, 130, 138, 150, 165, 168, 174, 180, 195, 198, 210, 228, 234, 252, 264, 270, 273, 285, 290, 294, 315, 318, 330, 345, 348, 354, 360, 385, 399, 402, 420, 434, 450, 462, 465, 468, 480, 504
Offset: 1
Keywords
Examples
omega(18) = 2 = 1 + 1 = omega(17) + omega(16), so 18 belongs to the sequence.
Links
- G. C. Greubel, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
omega[n_] := Length[FactorInteger[n]]; Select[Range[3, 10^3], omega[ # ] == omega[ # - 1] + omega[ # - 2] &]
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PARI
lista(kmax) = {my(o1 = omega(1), o2 = omega(2), o3); for(k = 3, kmax, o3 = omega(k); if(o3 == o1 + o2, print1(k, ", ")); o1 = o2; o2 = o3);} \\ Amiram Eldar, Sep 18 2024