21612906 has 48 divisors (see below), whose sum is σ = 55508544. Its totient is φ = 6174144.

The previous prime is 21612887. The next prime is 21612907. The reversal of 21612906 is 60921612.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a self number, because there is not a number n which added to its sum of digits gives 21612906.

It is not an unprimeable number, because it can be changed into a prime (21612907) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 226 + ... + 6578.

It is an arithmetic number, because the mean of its divisors is an integer number (1156428).

Almost surely, 2^21612906 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21612906, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27754272).

21612906 is an abundant number, since it is smaller than the sum of its proper divisors (33895638).

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

21612906 is an equidigital number, since it uses as much as digits as its factorization.

21612906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6377 (or 6365 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21612906 is about 4648.9682726386. The cubic root of 21612906 is about 278.5507859598.

The spelling of 21612906 in words is "twenty-one million, six hundred twelve thousand, nine hundred six".