21621870 has 64 divisors (see below), whose sum is σ = 58501440. Its totient is φ = 5681664.

The previous prime is 21621851. The next prime is 21621871. The reversal of 21621870 is 7812612.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621871) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 19162 + ... + 20258.

It is an arithmetic number, because the mean of its divisors is an integer number (914085).

Almost surely, 2^21621870 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21621870, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29250720).

21621870 is an abundant number, since it is smaller than the sum of its proper divisors (36879570).

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

21621870 is a wasteful number, since it uses less digits than its factorization.

21621870 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1186 (or 1180 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21621870 is about 4649.9322575711. The cubic root of 21621870 is about 278.5892904861.

The spelling of 21621870 in words is "twenty-one million, six hundred twenty-one thousand, eight hundred seventy".