A333052 Numbers m such that d(m) = d(m+1) and d(k) < d(m) for all k < m such that d(k) = d(k+1), where d(m) is the number of divisors of m (A000005).

2, 14, 44, 104, 735, 2295, 5264, 5984, 21735, 201824, 3341624, 6481475, 7316000, 49727600, 103488384, 205684479, 349167104, 391738599, 1921172175, 6110171144, 7616307699

Offset

1,1

Comments

The corresponding numbers of divisors are 2, 4, 6, 8, 12, 16, 20, 24, 32, 48, 64, 72, 96, 120, 128, 144, 160, 192, 240, 256, 288, ...

Links

Table of n, a(n) for n=1..21.

Example

2 is a term since (2, 3) is the first pair of consecutive numbers with the same number of divisors: d(2) = d(3) = 2.
14 is a term since d(14) = d(15) = 4 > d(2) = 2.
44 is a term since d(44) = d(45) = 6 > d(14) = 4.

Mathematica

seq = {}; dmax = 0; d1 = 1; Do[If[d1 == (d2 = DivisorSigma[0, n]) && d1 > dmax, dmax = d1; AppendTo[seq, n-1]]; d1 = d2, {n, 2, 10^4}]; seq

Crossrefs

Cf. A000005, A002182, A005237, A175143.

Sequence in context: A262963 A195960 A268684 * A075036 A212902 A091405

Adjacent sequences: A333049 A333050 A333051 * A333053 A333054 A333055

Keyword

nonn,more

Author

Amiram Eldar, Mar 06 2020

Status

approved