OFFSET
1,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
EXAMPLE
74 is the only semiprime in the interval [2*35, 2*38} = [70, 76] where 35, 38 are consecutive semiprimes.
PROG
(PARI) issemi(n)=bigomega(n)==2
precsemi(n)=while(!issemi(n--), ); n
nextsemi(n)=while(!issemi(n++), ); n
is(n)=if(!issemi(n), return(0)); my(a=precsemi(ceil(n/2)), b=nextsemi(n\2)); nextsemi(a)==b && nextsemi(2*a)==n && precsemi(2*b)==n \\ Charles R Greathouse IV, Mar 18 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Irina Gerasimova, Aug 18 2013
STATUS
approved