A374219 - OEIS

A374219

Composite numbers k such that A347381 obtains the same value for all divisors of k that are larger than one, where A347381 is the distance from n to the nearest common ancestor of n and sigma(n) in the Doudna-tree (A005940).

15, 77, 1403, 3127, 3139, 8383, 15247, 45151, 47263, 54053, 58339, 65473, 73813, 79567, 89951, 94957, 155011, 211621, 293323, 333961, 360883, 441901, 444853, 496597, 612893, 623659, 646367, 727393, 786193, 796723, 1334083, 1456813, 1572491, 2103379, 2139793, 2477509, 2668867, 2735539, 2826787, 2903591, 3121133

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OFFSET

1,1

COMMENTS

The first 47 terms are all semiprimes.

For three consecutive terms k=293323, 333961, 360883, A347381(k) = 89.

For three consecutive terms k=612893, 623659, 646367, A347381(k) = 134.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..47

Index entries for sequences related to sigma(n)

EXAMPLE

77 has divisors [7, 11, 77] that are larger than 1. For all of them, A347381 obtains value 3, therefore 77 is included in the sequence.