21001240 has 32 divisors (see below), whose sum is σ = 50888880. Its totient is φ = 7754112.

The previous prime is 21001187. The next prime is 21001247. The reversal of 21001240 is 4210012.

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001247) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19674 + ... + 20713.

Almost surely, 2^21001240 is an apocalyptic number.

21001240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21001240 is an abundant number, since it is smaller than the sum of its proper divisors (29887640).

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

21001240 is a wasteful number, since it uses less digits than its factorization.

21001240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40411 (or 40407 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 10.

The square root of 21001240 is about 4582.7109880506. The cubic root of 21001240 is about 275.8978477947.

Adding to 21001240 its reverse (4210012), we get a palindrome (25211252).

The spelling of 21001240 in words is "twenty-one million, one thousand, two hundred forty".