A049236 a(n) is the number of distinct prime factors of prime(n) + 2.

1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 2, 2, 1, 2, 1, 2, 1, 2, 2, 1, 2, 1, 2, 2, 2, 1, 3, 1, 2, 2, 2, 2, 1, 2, 1, 2, 2, 3, 1, 2, 1, 2, 1, 3, 1, 2, 2, 2, 1, 3, 2, 1, 1, 2, 2, 2, 1, 3, 2, 1, 3, 2, 2, 1, 3, 2, 2, 2, 1, 2, 2, 1, 2, 2, 2, 3, 2, 3, 2, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 2, 2, 2, 2, 2, 1, 3, 2, 2, 2, 2, 1, 2

Offset

1,6

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Formula

a(n) = A001221(A052147(n)). - Amiram Eldar, Sep 16 2024

Example

prime(27) = 103, prime(27) + 2 = 105 = 3*5*7 has 3 prime factors, so a(27) = 3.

Mathematica

Table[Length[FactorInteger[Prime[n] + 2]], {n, 1, 50}] (* G. C. Greubel, May 12 2017 *)

Prog

(PARI) a(n) = omega(prime(n) + 2); \\ Amiram Eldar, Sep 16 2024

Crossrefs

Cf. A000040, A001221, A001359, A052147, A064909, A064910, A064911.

Sequence in context: A282870 A106802 A269254 * A356229 A244259 A094840

Adjacent sequences: A049233 A049234 A049235 * A049237 A049238 A049239

Keyword

nonn,easy

Author

Labos Elemer

Status

approved