21131670 has 64 divisors (see below), whose sum is σ = 59222016. Its totient is φ = 4725120.

The previous prime is 21131653. The next prime is 21131689. The reversal of 21131670 is 7613112.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

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 31 ways as a sum of consecutive naturals, for example, 8800 + ... + 10940.

It is an arithmetic number, because the mean of its divisors is an integer number (925344).

Almost surely, 2^21131670 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21131670, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29611008).

21131670 is an abundant number, since it is smaller than the sum of its proper divisors (38090346).

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

21131670 is a wasteful number, since it uses less digits than its factorization.

21131670 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2205.

The product of its (nonzero) digits is 252, while the sum is 21.

The square root of 21131670 is about 4596.9196207896. The cubic root of 21131670 is about 276.4678318457.

Adding to 21131670 its reverse (7613112), we get a palindrome (28744782).

The spelling of 21131670 in words is "twenty-one million, one hundred thirty-one thousand, six hundred seventy".