OFFSET
1,1
COMMENTS
EXAMPLE
n=5 is in the sequence because 6*5-5 = 25 = 5*5 with x = y = 1.
n=10 is in the sequence because 6*10-5 = 55 = 5*11 with x=1, y=2.
MAPLE
isA016969 := proc(n)
(n mod 6)=5 ;
end proc:
isA016921 := proc(n)
(n mod 6)=1 ;
end proc:
isA091300 := proc(n)
(not isprime(n)) and isA016921(n) ;
end proc:
isA199860 := proc(n)
if isA091300(6*n-5) then
for d in numtheory[divisors](6*n-5) minus {1} do
if isA016969(d) and isA016969((6*n-5)/d) then
return true;
end if;
end do:
return false;
else
return false;
end if;
end proc:
for n from 5 to 210 do
if isA199860(n) then
printf("%d, ", n) ;
end if ;
end do; # R. J. Mathar, Nov 27 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eleonora Echeverri-Toro, Nov 11 2011
STATUS
approved