A335397 Starts of runs of 3 consecutive numbers that have an equal number of unitary and nonunitary divisors (A048109).

22625, 28375, 40472, 48248, 49624, 58374, 59750, 102248, 103624, 107702, 112374, 129623, 136214, 136375, 164295, 187623, 190375, 197910, 199624, 211624, 221750, 246616, 264248, 275750, 280231, 298375, 300806, 312471, 346086, 349623, 352375, 356375, 372248, 382374

Offset: 1

Author

Zak Seidov and Amiram Eldar, Jun 06 2020

Keywords

• nonn

Examples

			22625 is a term since 22625, 22626 and 22627 each have an equal number of unitary and nonunitary divisors. 22625 has 4 unitary divisors (1, 125, 181 and 22625) and 4 nonunitary divisors (5, 25, 905 and 4525), 22626 has 8 unitary divisors and 8 nonunitary divisors, and 22627 has 4 unitary divisors and 4 nonunitary divisors.
		

Links

• Zak Seidov, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A048109 and A335328.

Cf. A000005, A034444, A048105.

Programs

Mathematica

q[n_] := DivisorSigma[0, n] == 2^(PrimeNu[n] + 1); v = q /@ Range[3]; seq = {}; Do[v = Append[Drop[v, 1], q[k]]; If[And @@ v, AppendTo[seq, k - 2]], {k, 4, 2 * 10^5}]; seq