21312487 has 4 divisors (see below), whose sum is σ = 24357136. Its totient is φ = 18267840.

The previous prime is 21312463. The next prime is 21312493. The reversal of 21312487 is 78421312.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21312487 - 2¹¹ = 21310439 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312427) 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, 1522314 + ... + 1522327.

It is an arithmetic number, because the mean of its divisors is an integer number (6089284).

Almost surely, 2^21312487 is an apocalyptic number.

21312487 is a deficient number, since it is larger than the sum of its proper divisors (3044649).

21312487 is an equidigital number, since it uses as much as digits as its factorization.

21312487 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3044648.

The product of its digits is 2688, while the sum is 28.

The square root of 21312487 is about 4616.5449201757. The cubic root of 21312487 is about 277.2541425476.

Adding to 21312487 its reverse (78421312), we get a palindrome (99733799).

The spelling of 21312487 in words is "twenty-one million, three hundred twelve thousand, four hundred eighty-seven".