The On-Line Encyclopedia of Integer Sequences (OEIS)

A335328 revision #14

A335328

Number k such that both k and k+1 have an equal number of unitary and nonunitary divisors.

135, 296, 343, 375, 1160, 1431, 1592, 1624, 2295, 2456, 2727, 3429, 3591, 3624, 3752, 3992, 4023, 4184, 4887, 4913, 5048, 5144, 5319, 5480, 6183, 6344, 6375, 6858, 7479, 7624, 7640, 7749, 7911, 8072, 8375, 8936, 9207, 9368, 9624, 10071, 10232, 10375, 10503, 10632

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OFFSET

1,1

COMMENTS

Terms k such that k+1 is also in this sequence are 22625, 28375, 40472, ...

LINKS

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

EXAMPLE

135 is a term since both 135 and 136 have 4 unitary divisors and 4 nonunitary divisors.

MATHEMATICA

seqQ[n_] := DivisorSigma[0, n] == 2^(PrimeNu[n] + 1); q1 = seqQ[1]; s = {}; Do[q2 = seqQ[n]; If[q1 && q2, AppendTo[s, n-1]]; q1 = q2, {n, 2, 10^4}]; s (* typo corrected by Zak Seidov, Jun 04 2020 *)

CROSSREFS

Cf. A000005, A034444, A048105, A048109.

Sequence in context: A374461 A176313 A372691 * A215173 A225360 A328651

Adjacent sequences: A335325 A335326 A335327 * A335329 A335330 A335331

KEYWORD

nonn

AUTHOR

Amiram Eldar, Jun 01 2020

STATUS

editing