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A199859
Numbers k such that 6k-5 is a composite number of the form (6x-5)*(6y-5) when x or y is not equal to 1 except for k=1.
2
1, 9, 16, 23, 29, 30, 37, 42, 44, 51, 55, 58, 61, 65, 68, 72, 79, 80, 81, 86, 93, 94, 99, 100, 105, 107, 114, 118, 120, 121, 128, 130, 133, 135, 137, 142, 146, 149, 155, 156, 159, 161, 163, 170, 172, 175, 177, 180, 184, 185, 191, 192, 194, 198, 205, 211, 212
OFFSET
0,2
COMMENTS
Numbers whose associate in A091300 has at least one nontrivial factorization into two factors of A016921.
MAPLE
isA016921 := proc(n)
(n mod 6)=1 ;
end proc:
isA091300 := proc(n)
(not isprime(n)) and isA016921(n) ;
end proc:
isA199859 := proc(n)
if n = 1 then
return true;
elif isA091300(6*n-5) then
for d in numtheory[divisors](6*n-5) minus {1, 6*n-5} do
if isA016921(d) and isA016921((6*n-5)/d) then
return true;
end if;
end do:
return false;
else
return false;
end if;
end proc:
for n from 1 to 210 do
if isA199859(n) then
printf("%d, ", n) ;
end if ;
end do; # R. J. Mathar, Nov 25 2011
CROSSREFS
Cf. A091300.
Sequence in context: A045911 A287186 A134256 * A046463 A003332 A345793
KEYWORD
nonn,easy
AUTHOR
STATUS
approved