21090906 has 24 divisors (see below), whose sum is σ = 45792864. Its totient is φ = 7015560.

The previous prime is 21090899. The next prime is 21090913. The reversal of 21090906 is 60909012.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21090899) and next prime (21090913).

It is a self number, because there is not a number n which added to its sum of digits gives 21090906.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10741 + ... + 12551.

It is an arithmetic number, because the mean of its divisors is an integer number (1908036).

Almost surely, 2^21090906 is an apocalyptic number.

21090906 is an abundant number, since it is smaller than the sum of its proper divisors (24701958).

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

21090906 is a wasteful number, since it uses less digits than its factorization.

21090906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2466 (or 2463 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 21090906 is about 4592.4836417782. The cubic root of 21090906 is about 276.2899441977.

Adding to 21090906 its reverse (60909012), we get a palindrome (81999918).

It can be divided in two parts, 2 and 1090906, that multiplied together give a palindrome (2181812).

The spelling of 21090906 in words is "twenty-one million, ninety thousand, nine hundred six".