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%I #14 Sep 18 2015 04:29:37
%S 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,
%T 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,
%U 5,5,0,3,3,0,5,5,5,5,0,3,3,0,0,0,4,4,4
%N Difference between (least semiprime >= n) and (largest semiprime <= n).
%C a(n) = 0 if and only if n is semiprime.
%H Arkadiusz Wesolowski, <a href="/A200927/b200927.txt">Table of n, a(n) for n = 4..10000</a>
%p A106325 := proc(n)
%p for a from n do
%p if numtheory[bigomega](a) = 2 then
%p return a;
%p end if;
%p end do:
%p end proc;
%p prevSpr := proc(n)
%p for a from n by -1 do
%p if numtheory[bigomega](a) = 2 then
%p return a;
%p end if;
%p end do:
%p end proc;
%p A200927 := proc(n)
%p A106325(n)-prevSpr(n) ;
%p end proc:
%p seq(A200927(n),n=4..80) ; # _R. J. Mathar_, Nov 26 2011
%t Table[a = b = 0; While[! PrimeOmega[n - a] == 2, a++]; While[! PrimeOmega[n + b] == 2, b++]; a + b, {n, 4, 100}]
%Y Cf. A001358, A065516.
%K nonn
%O 4,2
%A _Arkadiusz Wesolowski_, Nov 24 2011
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