21660404 has 6 divisors (see below), whose sum is σ = 37905714. Its totient is φ = 10830200.

The previous prime is 21660389. The next prime is 21660407. The reversal of 21660404 is 40406612.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 20268004 + 1392400 = 4502^2 + 1180^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21660404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660407) 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, 2707547 + ... + 2707554.

It is an arithmetic number, because the mean of its divisors is an integer number (6317619).

Almost surely, 2^21660404 is an apocalyptic number.

It is an amenable number.

21660404 is a deficient number, since it is larger than the sum of its proper divisors (16245310).

21660404 is a wasteful number, since it uses less digits than its factorization.

21660404 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5415105 (or 5415103 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 23.

The square root of 21660404 is about 4654.0739143250. The cubic root of 21660404 is about 278.7546907453.

The spelling of 21660404 in words is "twenty-one million, six hundred sixty thousand, four hundred four".