login
A183147
1 together with the numbers with property that at least two successive of their divisors are odd or even.
1
1, 3, 4, 5, 7, 8, 9, 11, 12, 13, 15, 16, 17, 19, 20, 21, 23, 24, 25, 27, 28, 29, 30, 31, 32, 33, 35, 36, 37, 39, 40, 41, 43, 44, 45, 47, 48, 49, 51, 52, 53, 55, 56, 57, 59, 60, 61, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 75, 76, 77, 79, 80, 81, 83, 84, 85, 87, 88, 89, 90, 91, 92, 93, 95, 96, 97, 99, 100
OFFSET
1,2
EXAMPLE
12 is in the sequence because its divisors are 1, 2, 3, 4, 6, 12 and then we can see that the successive divisors 4, 6, and 12 are even numbers.
MAPLE
isA183147 := proc(n)
local di, i ;
if n = 1 then
return true;
end if;
di := sort(convert(numtheory[divisors](n), list)) ;
for i from 1 to nops(di)-1 do
if (op(i+1, di)-op(i, di)) mod 2 = 0 then
return true;
end if;
end do;
return false;
end proc:
for n from 1 to 100 do
if isA183147(n) then
printf("%d, ", n);
end if;
end do; # R. J. Mathar, Sep 30 2011
CROSSREFS
Complement of A182991, for n > 1.
Cf. A182996.
Sequence in context: A285958 A179779 A284679 * A074227 A122906 A042965
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Aug 04 2011
STATUS
approved