A075033 Numbers n such that tau(n) <= tau(n+1) <= tau(n+2) <= tau(n+3) where tau(n) = number of divisors of n.

1, 13, 25, 33, 37, 61, 73, 85, 93, 97, 121, 133, 141, 145, 157, 187, 193, 201, 205, 213, 217, 229, 241, 242, 243, 253, 277, 283, 301, 361, 373, 393, 397, 421, 427, 445, 453, 457, 481, 537, 541, 547, 603, 613, 633, 661, 662, 663, 697, 723, 733, 745, 757, 781

Offset

1,2

Links

Karl V. Keller, Jr., Table of n, a(n) for n = 1..10000

Mathematica

With[{s = Partition[Differences@ Array[DivisorSigma[0, #] &, 800], 3, 1]}, Position[s, _?(AllTrue[#, # >= 0 &] &), {1}, Heads -> False][[All, 1]]] (* Michael De Vlieger, Jun 28 2020 *)

Prog

(Python)
from sympy import divisor_count as tau
[n for n in range(1, 801) if tau(n) <= tau(n+1) <= tau(n+2) <= tau(n+3)] # Karl V. Keller, Jr., Jul 10 2020

Crossrefs

Cf. A000005, A075032, A075034, A075035.

Sequence in context: A032478 A280925 A161603 * A017533 A309809 A264732

Adjacent sequences: A075030 A075031 A075032 * A075034 A075035 A075036

Keyword

nonn

Author

Amarnath Murthy, Sep 02 2002

Extensions

Added missing term and a(11)-a(54) from Donovan Johnson, Jun 15 2009

Status

approved