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A383468

Semiprimes s = A001358(k) such that k, s - k and s + k are also semiprimes.

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

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OFFSET

1,1

COMMENTS

Except for a(1) = 10 = A001358(4), s and k always have different parities.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

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;

od:

CROSSREFS

Cf. A001358. A383469.

Sequence in context: A339314 A166626 A238759 * A278349 A114703 A134515