21281670 has 96 divisors (see below), whose sum is σ = 59724000. Its totient is φ = 5391936.

The previous prime is 21281669. The next prime is 21281677. The reversal of 21281670 is 7618212.

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 (21281677) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 142756 + ... + 142904.

It is an arithmetic number, because the mean of its divisors is an integer number (622125).

Almost surely, 2^21281670 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21281670, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29862000).

21281670 is an abundant number, since it is smaller than the sum of its proper divisors (38442330).

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

21281670 is a wasteful number, since it uses less digits than its factorization.

21281670 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 211 (or 182 counting only the distinct ones).

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

The square root of 21281670 is about 4613.2060435233. The cubic root of 21281670 is about 277.1204453026.

Adding to 21281670 its reverse (7618212), we get a palindrome (28899882).

The spelling of 21281670 in words is "twenty-one million, two hundred eighty-one thousand, six hundred seventy".