21651604 has 18 divisors (see below), whose sum is σ = 41030430. Its totient is φ = 9992736.

The previous prime is 21651593. The next prime is 21651607. The reversal of 21651604 is 40615612.

It can be written as a sum of positive squares in 3 ways, for example, as 2729104 + 18922500 = 1652^2 + 4350^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651607) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 15339 + ... + 16690.

Almost surely, 2^21651604 is an apocalyptic number.

It is an amenable number.

21651604 is a deficient number, since it is larger than the sum of its proper divisors (19378826).

21651604 is a wasteful number, since it uses less digits than its factorization.

21651604 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32059 (or 32044 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21651604 is about 4653.1284100055. The cubic root of 21651604 is about 278.7169356238.

The spelling of 21651604 in words is "twenty-one million, six hundred fifty-one thousand, six hundred four".