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URL: https://oeis.org/A383468

⇱ A383468 - OEIS


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A383468
Semiprimes s = A001358(k) such that k, s - k and s + k are also semiprimes.
2
10, 15, 141, 166, 274, 298, 299, 687, 995, 1115, 1227, 1299, 1345, 1891, 1945, 2194, 2661, 2998, 3093, 3287, 3566, 3781, 3902, 4174, 4262, 4497, 4798, 5378, 5414, 5758, 6609, 7094, 7666, 8354, 8434, 9566, 10041, 10342, 11051, 11091, 11486, 11582, 11702, 12279, 12574, 13154, 13346, 13387, 13466
OFFSET
1,1
COMMENTS
Except for a(1) = 10 = A001358(4), s and k always have different parities.
LINKS
FORMULA
a(n) = A001358(A383469(n)).
EXAMPLE
a(3) = 141 is a term because 141 = 3 * 47 = A001358(46) is a semiprime and 46 = 2 * 23, 141 - 46 = 95 = 5 * 19 and 141 + 46 = 187 = 11 * 17 are all semiprimes.
MAPLE
k:= 0: R:= NULL: count:= 0:
for s from 1 while count < 100 do
if numtheory:-bigomega(s) = 2 then
k:= k+1;
if andmap(t -> numtheory:-bigomega(t) = 2, [k, s-k, s+k]) then
R:= R, s; count:= count+1;
fi
fi;
od:
R;
CROSSREFS
Sequence in context: A339314 A166626 A238759 * A278349 A114703 A134515
KEYWORD
nonn
AUTHOR
Zak Seidov and Robert Israel, Apr 27 2025
STATUS
approved