21603866 has 4 divisors (see below), whose sum is σ = 32405802. Its totient is φ = 10801932.

The previous prime is 21603863. The next prime is 21603871. The reversal of 21603866 is 66830612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 20511841 + 1092025 = 4529^2 + 1045^2 .

It is a super-2 number, since 2×21603866² = 933454052291912, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21603863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5400965 + ... + 5400968.

Almost surely, 2^21603866 is an apocalyptic number.

21603866 is a deficient number, since it is larger than the sum of its proper divisors (10801936).

21603866 is a wasteful number, since it uses less digits than its factorization.

21603866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10801935.

The product of its (nonzero) digits is 10368, while the sum is 32.

The square root of 21603866 is about 4647.9959122185. The cubic root of 21603866 is about 278.5119441945.

The spelling of 21603866 in words is "twenty-one million, six hundred three thousand, eight hundred sixty-six".