21351906 has 12 divisors (see below), whose sum is σ = 46262502. Its totient is φ = 7117296.

The previous prime is 21351899. The next prime is 21351907. The reversal of 21351906 is 60915312.

It can be written as a sum of positive squares in only one way, i.e., 17514225 + 3837681 = 4185^2 + 1959^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21351906.

It is not an unprimeable number, because it can be changed into a prime (21351907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 593091 + ... + 593126.

Almost surely, 2^21351906 is an apocalyptic number.

21351906 is an abundant number, since it is smaller than the sum of its proper divisors (24910596).

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

21351906 is a wasteful number, since it uses less digits than its factorization.

21351906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1186225 (or 1186222 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 27.

The square root of 21351906 is about 4620.8122662580. The cubic root of 21351906 is about 277.4249711939.

The spelling of 21351906 in words is "twenty-one million, three hundred fifty-one thousand, nine hundred six".