21399636 has 24 divisors (see below), whose sum is σ = 50317344. Its totient is φ = 7078240.

The previous prime is 21399563. The next prime is 21399649. The reversal of 21399636 is 63699312.

It is a junction number, because it is equal to n+sod(n) for n = 21399594 and 21399603.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5235 + ... + 8378.

It is an arithmetic number, because the mean of its divisors is an integer number (2096556).

Almost surely, 2^21399636 is an apocalyptic number.

It is an amenable number.

21399636 is an abundant number, since it is smaller than the sum of its proper divisors (28917708).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21399636 is a wasteful number, since it uses less digits than its factorization.

21399636 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13751 (or 13749 counting only the distinct ones).

The product of its digits is 52488, while the sum is 39.

The square root of 21399636 is about 4625.9740595900. The cubic root of 21399636 is about 277.6315357264.

It can be divided in two parts, 2139963 and 6, that multiplied together give a triangular number (12839778 = T₅₀₆₇).

The spelling of 21399636 in words is "twenty-one million, three hundred ninety-nine thousand, six hundred thirty-six".