OFFSET
1,1
COMMENTS
Equally: odd composite numbers n for which A246702((n+1)/2) = 2.
EXAMPLE
35 = 5*7 is an odd composite. Only cases where 2^k - 1 (with k in range 1 .. 35^2 - 1 = 1 .. 1224) is a multiple of 35 are k = 420 and k = 840, thus 35 is included in this sequence.
MAPLE
isA249819 := proc(n)
if isprime(n) or n=1 then
false;
else
ct := 0 ;
for k from 1 to n^2-1 do
if modp(2 &^ k-1, n^2) = 0 then
ct := ct+1 ;
end if;
if ct > 2 then
return false;
end if;
end do:
return is(ct=2) ;
end if;
end proc:
for n from 1 to 1100 do
if isA249819(n) then
printf("%d, \n", n) ;
end if;
end do: # R. J. Mathar, Nov 16 2014
PROG
(Scheme, with Antti Karttunen's IntSeq-library)
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 15 2014
STATUS
approved