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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).
3
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
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.
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.
PROG
(PARI) isA374219(n) = if(1==n || isprime(n), 0, my(w=A347381(n)); fordiv(n, d, if(d>1 && A347381(d)!=w, return(0))); (1));
CROSSREFS
Subsequence of A374218.
Sequence in context: A257925 A205433 A303097 * A128272 A180579 A081591
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jul 07 2024
STATUS
approved