21215340 has 72 divisors (see below), whose sum is σ = 65873808. Its totient is φ = 5523840.

The previous prime is 21215339. The next prime is 21215399. The reversal of 21215340 is 4351212.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6370 + ... + 9110.

It is an arithmetic number, because the mean of its divisors is an integer number (914914).

Almost surely, 2^21215340 is an apocalyptic number.

21215340 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21215340, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32936904).

21215340 is an abundant number, since it is smaller than the sum of its proper divisors (44658468).

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

21215340 is a wasteful number, since it uses less digits than its factorization.

21215340 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2799 (or 2794 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21215340 is about 4606.0112896084. The cubic root of 21215340 is about 276.8322390808.

Adding to 21215340 its reverse (4351212), we get a palindrome (25566552).

The spelling of 21215340 in words is "twenty-one million, two hundred fifteen thousand, three hundred forty".