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A075033 Numbers n such that tau(n) <= tau(n+1) <= tau(n+2) <= tau(n+3) where tau(n) = number of divisors of n. 4
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 13 02:09 EDT 2020. Contains 336441 sequences. (Running on oeis4.)