21240087 has 8 divisors (see below), whose sum is σ = 30894720. Its totient is φ = 12872760.

The previous prime is 21240073. The next prime is 21240097. The reversal of 21240087 is 78004212.

21240087 = 224² + 225² + ... + 421².

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21240087 - 2⁸ = 21239831 is a prime.

It is a super-2 number, since 2×21240087² = 902282591535138, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21240097) 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, 321787 + ... + 321852.

It is an arithmetic number, because the mean of its divisors is an integer number (3861840).

Almost surely, 2^21240087 is an apocalyptic number.

21240087 is a deficient number, since it is larger than the sum of its proper divisors (9654633).

21240087 is a wasteful number, since it uses less digits than its factorization.

21240087 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 643653.

The product of its (nonzero) digits is 896, while the sum is 24.

The square root of 21240087 is about 4608.6968874075. The cubic root of 21240087 is about 276.9398358388.

Adding to 21240087 its reverse (78004212), we get a palindrome (99244299).

The spelling of 21240087 in words is "twenty-one million, two hundred forty thousand, eighty-seven".