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A361611
Lexicographically least increasing sequence of semiprimes a(n) such that a(n) - a(n-1) and a(n) + a(n-1) are also semiprimes.
5
4, 10, 25, 94, 115, 206, 221, 298, 391, 478, 511, 526, 551, 586, 655, 694, 703, 758, 779, 934, 949, 974, 989, 993, 1126, 1159, 1418, 1513, 1522, 1555, 1594, 1603, 1658, 1679, 1718, 1769, 2018, 2051, 2066, 2105, 2174, 2195, 2234, 2319, 2462, 2501, 2578, 2587, 2846, 2867, 2906, 2931, 2986, 3007
OFFSET
1,1
LINKS
EXAMPLE
a(3) = 25 because with a(2) = 10, 25, 25 - 10 = 15 and 25 + 10 = 35 are all semiprimes, and none of the semiprimes between 10 and 25 work.
MAPLE
R:= 4: count:= 0: x:= 4:
for i from 5 while count < 100 do
if andmap(t -> numtheory:-bigomega(t)=2, [i, i+x, i-x]) then
R:= R, i; x:= i; count:= count+1
fi
od:
R;
MATHEMATICA
s = {m=4}; Do[p = m + 4; While[{2, 2, 2} != PrimeOmega[{p, m + p, p -
m}], p++]; AppendTo[s, m = p], {100}]; s
CROSSREFS
Cf. A001358.
Sequence in context: A097136 A049348 A282389 * A145775 A283958 A335637
KEYWORD
nonn
AUTHOR
Zak Seidov and Robert Israel, Mar 17 2023
STATUS
approved