21687464 has 8 divisors (see below), whose sum is σ = 40664010. Its totient is φ = 10843728.

The previous prime is 21687373. The next prime is 21687473. The reversal of 21687464 is 46478612.

It can be written as a sum of positive squares in only one way, i.e., 13032100 + 8655364 = 3610^2 + 2942^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1355459 + ... + 1355474.

Almost surely, 2^21687464 is an apocalyptic number.

It is an amenable number.

21687464 is a deficient number, since it is larger than the sum of its proper divisors (18976546).

21687464 is a wasteful number, since it uses less digits than its factorization.

21687464 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2710939 (or 2710935 counting only the distinct ones).

The product of its digits is 64512, while the sum is 38.

The square root of 21687464 is about 4656.9801373852. The cubic root of 21687464 is about 278.8707237142.

The spelling of 21687464 in words is "twenty-one million, six hundred eighty-seven thousand, four hundred sixty-four".