21387906 has 24 divisors (see below), whose sum is σ = 47939580. Its totient is φ = 6883296.

The previous prime is 21387893. The next prime is 21387929. The reversal of 21387906 is 60978312.

It can be written as a sum of positive squares in 2 ways, for example, as 19000881 + 2387025 = 4359^2 + 1545^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 19965 + ... + 21008.

Almost surely, 2^21387906 is an apocalyptic number.

21387906 is an abundant number, since it is smaller than the sum of its proper divisors (26551674).

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

21387906 is a wasteful number, since it uses less digits than its factorization.

21387906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41010 (or 41007 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 21387906 is about 4624.7060447125. The cubic root of 21387906 is about 277.5807994565.

The spelling of 21387906 in words is "twenty-one million, three hundred eighty-seven thousand, nine hundred six".