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, 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

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: A238400 A266276 A088252 * A196303 A048979 A201363

Adjacent sequences: A334018 A334019 A334020 * A334022 A334023 A334024

Keyword

nonn

Author

Amiram Eldar, Apr 12 2020

Status

approved