21251868 has 48 divisors (see below), whose sum is σ = 54552960. Its totient is φ = 6385600.

The previous prime is 21251863. The next prime is 21251873. The reversal of 21251868 is 86815212.

It is an interprime number because it is at equal distance from previous prime (21251863) and next prime (21251873).

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21251863) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16678 + ... + 17906.

It is an arithmetic number, because the mean of its divisors is an integer number (1136520).

Almost surely, 2^21251868 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21251868, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27276480).

21251868 is an abundant number, since it is smaller than the sum of its proper divisors (33301092).

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

21251868 is a wasteful number, since it uses less digits than its factorization.

21251868 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1378 (or 1376 counting only the distinct ones).

The product of its digits is 7680, while the sum is 33.

The square root of 21251868 is about 4609.9748372415. The cubic root of 21251868 is about 276.9910287424.

It can be divided in two parts, 2125 and 1868, that added together give a palindrome (3993).

The spelling of 21251868 in words is "twenty-one million, two hundred fifty-one thousand, eight hundred sixty-eight".