A335398 Starts of runs of 4 consecutive numbers that have an equal number of unitary and nonunitary divisors (A048109).

2068373, 2948373, 3571749, 3916374, 4730373, 4757750, 6755750, 8109125, 11290872, 12248872, 13071750, 13648311, 13903623, 15278247, 15448374, 15449749, 16793622, 17446374, 17991125, 19407624, 20080248, 20250375, 21594248, 22577750, 24190758, 25297622, 26140373

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

2068373 is a term since 2068373, 2068374, 2068375 and 2068376 each have an equal number of unitary and nonunitary divisors. 2068373 and 2068375 each have 4 unitary divisors and 4 nonunitary divisors, 2068374 has 32 unitary divisors and 32 nonunitary divisors, and 2068376 has 8 unitary divisors and 8 nonunitary divisors.

Mathematica

q[n_] := DivisorSigma[0, n] == 2^(PrimeNu[n] + 1); v = q /@ Range[4]; seq = {}; Do[v = Append[Drop[v, 1], q[k]]; If[And @@ v, AppendTo[seq, k - 3]], {k, 5, 10^7}]; seq

Crossrefs

Subsequence of A048109, A335328 and A335397.

Cf. A000005, A034444, A048105.

Sequence in context: A186915 A186907 A186906 * A155125 A155126 A234469

Adjacent sequences: A335395 A335396 A335397 * A335399 A335400 A335401

Keyword

nonn

Author

Zak Seidov and Amiram Eldar, Jun 06 2020

Status

approved