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A367496
Semiprimes k such that 2 * k - 1 and 2 * k + 1 are also semiprimes.
1
25, 46, 93, 118, 133, 145, 161, 206, 226, 235, 259, 267, 291, 295, 334, 335, 361, 377, 395, 407, 447, 497, 529, 573, 579, 583, 669, 674, 685, 694, 695, 781, 843, 898, 899, 921, 926, 961, 979, 1059, 1079, 1114, 1115, 1142, 1159, 1214, 1227, 1241, 1257, 1285, 1286, 1294, 1315, 1379, 1393, 1405
OFFSET
1,1
COMMENTS
One of the three semiprimes k, 2 * k - 1 and 2 * k + 1 is 3 times a prime.
LINKS
EXAMPLE
a(3) = 93 is a term because 93 = 3 * 31, 2 * 93 - 1 = 185 = 5 * 37 and 2 * 93 + 1 = 187 = 11 * 17 are semiprimes.
MAPLE
select(t -> numtheory:-bigomega(t) = 2 and numtheory:-bigomega(2*t-1) = 2 and numtheory:-bigomega(2*t+1) = 2, [$1..2000]);
MATHEMATICA
Select[Range[1410], PrimeOmega[#]==PrimeOmega[2#+1]==PrimeOmega[2#-1]==2 &] (* Stefano Spezia, Nov 20 2023 *
CROSSREFS
Cf. A001358. Intersection of A111153 and A111168.
Sequence in context: A192261 A038811 A028505 * A154082 A216869 A143278
KEYWORD
nonn
AUTHOR
Zak Seidov and Robert Israel, Nov 20 2023
STATUS
approved