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A109290
Composite numbers which are not of the forms p*q -+ 1, where p and q are (not necessarily distinct) primes.
4
4, 6, 12, 18, 28, 30, 42, 44, 46, 49, 51, 55, 60, 62, 65, 69, 72, 74, 77, 80, 82, 91, 98, 99, 100, 102, 104, 106, 108, 111, 115, 125, 126, 129, 136, 138, 148, 150, 152, 153, 155, 161, 164, 166, 169, 171, 172, 174, 175, 180, 183, 185, 187, 189, 190, 192, 194, 196
OFFSET
1,1
LINKS
MAPLE
filter:= proc(n)
if n::even then numtheory:-bigomega(n+1) <> 2 and numtheory:-bigomega(n-1) <> 2
elif n mod 4 = 1 then not isprime(n) and not isprime((n+1)/2)
else not isprime(n) and not isprime((n-1)/2)
fi
end proc:
select(filter, [$4..200]); # Robert Israel, Apr 20 2021
MATHEMATICA
bo[n_] := Plus @@ Last /@ FactorInteger[n]; Select[Range[2, 200], ! (PrimeQ[ # ] || bo[ # - 1] == 2 || bo[ # + 1] == 2) &] (* Ray Chandler, Aug 27 2005 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Teofilatto, Aug 20 2005
EXTENSIONS
Corrected and extended by Ray Chandler, Aug 27 2005
STATUS
approved