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A200927 Difference between (least semiprime >= n) and (largest semiprime <= n). 1
0, 2, 0, 3, 3, 0, 0, 4, 4, 4, 0, 0, 6, 6, 6, 6, 6, 0, 0, 3, 3, 0, 0, 7, 7, 7, 7, 7, 7, 0, 0, 0, 3, 3, 0, 0, 7, 7, 7, 7, 7, 7, 0, 3, 3, 0, 2, 0, 4, 4, 4, 0, 2, 0, 0, 4, 4, 4, 0, 3, 3, 0, 4, 4, 4, 0, 5, 5, 5, 5, 0, 3, 3, 0, 5, 5, 5, 5, 0, 3, 3, 0, 0, 0, 4, 4, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,2

COMMENTS

a(n) = 0 if and only if n is semiprime.

LINKS

Arkadiusz Wesolowski, Table of n, a(n) for n = 4..10000

MAPLE

A106325 := proc(n)

    for a from n do

        if numtheory[bigomega](a) = 2 then

            return a;

        end if;

    end do:

end proc;

prevSpr := proc(n)

    for a from n by -1 do

        if numtheory[bigomega](a) = 2 then

            return a;

        end if;

    end do:

end proc;

A200927 := proc(n)

    A106325(n)-prevSpr(n) ;

end proc:

seq(A200927(n), n=4..80) ; # R. J. Mathar, Nov 26 2011

MATHEMATICA

Table[a = b = 0; While[! PrimeOmega[n - a] == 2, a++]; While[! PrimeOmega[n + b] == 2, b++]; a + b, {n, 4, 100}]

CROSSREFS

Cf. A001358, A065516.

Sequence in context: A219187 A049799 A087985 * A258817 A004557 A088276

Adjacent sequences:  A200924 A200925 A200926 * A200928 A200929 A200930

KEYWORD

nonn

AUTHOR

Arkadiusz Wesolowski, Nov 24 2011

STATUS

approved

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Last modified May 6 17:38 EDT 2021. Contains 343586 sequences. (Running on oeis4.)