OFFSET
1,2
FORMULA
a(n) = 1 + pi(n) - pi(n / 2) + [n >= 4], where pi denotes the prime counting function (A000720, generalized to reals), and [] the Iverson bracket.
MATHEMATICA
A[n_] := Length[
ConnectedComponents[
AdjacencyGraph[Map[Boole[# != 1] &, Array[GCD, {n, n}], {2}]]]]
Table[A[n], {n, 1, 107}]
PROG
(PARI) a(n) = 1 + primepi(n) - primepi(n / 2) + (n >= 4); \\ Michel Marcus, Jan 09 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Luc Rousseau, Jan 01 2018
STATUS
approved