login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A334021 Numbers k such that s(k) = s(k+1) = s(k+2), where s(k) is the sum of unitary divisors of k that are smaller than sqrt(k) (A334019). 2
2, 3, 7, 1420, 2505, 11860, 64060, 64485, 113413, 158020, 205365, 332658, 465272, 522764, 611085, 614538, 635053, 664033, 748484, 771138, 839213, 881565, 1011793, 1090788, 1190685, 1248645, 1306605, 1488088, 1607367, 1613190, 1836018, 1884914, 1911940, 2286913 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..1000

EXAMPLE

2 is a term since A334019(2) = A334019(3) = A334019(4) = 1.

MATHEMATICA

s[n_] := DivisorSum[n, # &, #^2 < n && CoprimeQ[#, n/#] &]; seq={}; s1 = s[1]; s2 = s[2]; Do[s3 = s[n]; If[s1 == s2 && s2 == s3, AppendTo[seq, n - 2]]; s1 = s2; s2 = s3, {n, 3, 10^5}]; seq

CROSSREFS

Cf. A324310, A334019, A334020.

Sequence in context: A266276 A088252 A320432 * A196303 A048979 A088332

Adjacent sequences:  A334018 A334019 A334020 * A334022 A334023 A334024

KEYWORD

nonn

AUTHOR

Amiram Eldar, Apr 12 2020

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 4 14:51 EDT 2020. Contains 335448 sequences. (Running on oeis4.)