OFFSET
1,1
COMMENTS
One of the three semiprimes k, 2 * k - 1 and 2 * k + 1 is 3 times a prime.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
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
KEYWORD
nonn
AUTHOR
Zak Seidov and Robert Israel, Nov 20 2023
STATUS
approved