OFFSET
1,10
COMMENTS
Conjecture: a(n)>0 for n>5.
LINKS
Michel Lagneau, Table of n, a(n) for n = 1..1000
EXAMPLE
a(12)=3 as prime(12) = 37 = (9+65)/2 = (25+49)/2 =(35+39)/2 where 9, 25, 35, 39, 49 and 65 are semiprime.
MAPLE
with(numtheory):for n from 1 to 100 do:c:=0:p:=ithprime(n):for m from 1 to p-1 do:p1:=p-m:p2:=p+m:if bigomega(p1)=2 and bigomega(p2)=2 then c:=c+1:else fi:od:printf(`%d, `, c):od:
MATHEMATICA
Reap[For[n=1, n <= 100, n++, c=0; p = Prime[n]; For[m=1, m <= p-1, m++, p1 = p-m; p2 = p+m; If[PrimeOmega[p1] == 2 && PrimeOmega[p2] == 2 , c = c+1]]; Print[c]; Sow[c]]][[2, 1]] (* Jean-François Alcover, Mar 23 2015, translated from Maple *)
PROG
(Haskell)
a253138 n = sum $ map a064911 $
takeWhile (> 0) $ map (2 * p -) $ dropWhile (< p) a001358_list
where p = a000040 n
-- Reinhard Zumkeller, Mar 27 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Mar 23 2015
STATUS
approved