21145240 has 16 divisors (see below), whose sum is σ = 47576880. Its totient is φ = 8458080.

The previous prime is 21145213. The next prime is 21145249. The reversal of 21145240 is 4254112.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21145249) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 264276 + ... + 264355.

It is an arithmetic number, because the mean of its divisors is an integer number (2973555).

Almost surely, 2^21145240 is an apocalyptic number.

21145240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21145240 is an abundant number, since it is smaller than the sum of its proper divisors (26431640).

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

21145240 is a wasteful number, since it uses less digits than its factorization.

21145240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 528642 (or 528638 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 19.

The square root of 21145240 is about 4598.3953723011. The cubic root of 21145240 is about 276.5269984221.

Adding to 21145240 its reverse (4254112), we get a palindrome (25399352).

It can be divided in two parts, 211 and 45240, that added together give a triangular number (45451 = T₃₀₁).

The spelling of 21145240 in words is "twenty-one million, one hundred forty-five thousand, two hundred forty".