OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(3)=20 is a member of the sequence because 20 is neither prime nor semiprime, 20-1=19 is prime and 20+1=21 is semiprime.
MAPLE
issp:= proc(n) numtheory:-bigomega(n)=2 end proc:
filter:= proc(n)
if isprime(n) or issp(n) then return false fi;
if isprime(n-1) then issp(n+1)
else isprime(n+1) and issp(n-1)
fi;
end proc:
select(filter, [seq(i, i=2..1000, 2)]);
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Sep 13 2019
STATUS
approved