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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
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
Sequence in context: A219187 A049799 A087985 * A372820 A372819 A372818
KEYWORD
nonn
AUTHOR
STATUS
approved