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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Numbers whose associate in A091300 has at least one nontrivial factorization into two factors of A016921.

LINKS

Table of n, a(n) for n=0..56.

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 A091571

Adjacent sequences:  A199856 A199857 A199858 * A199860 A199861 A199862

KEYWORD

nonn,easy

AUTHOR

Eleonora Echeverri-Toro, Nov 11 2011

STATUS

approved

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Last modified April 10 02:39 EDT 2020. Contains 333392 sequences. (Running on oeis4.)