21312819 has 18 divisors (see below), whose sum is σ = 33839988. Its totient is φ = 12916200.

The previous prime is 21312793. The next prime is 21312829. The reversal of 21312819 is 91821312.

It is not a de Polignac number, because 21312819 - 2⁵ = 21312787 is a prime.

It is a super-2 number, since 2×21312819² = 908472507453522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21312792 and 21312801.

It is not an unprimeable number, because it can be changed into a prime (21312829) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 8697 + ... + 10874.

Almost surely, 2^21312819 is an apocalyptic number.

21312819 is a deficient number, since it is larger than the sum of its proper divisors (12527169).

21312819 is a wasteful number, since it uses less digits than its factorization.

21312819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19599 (or 19585 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 21312819 is about 4616.5808776626. The cubic root of 21312819 is about 277.2555822028.

It can be divided in two parts, 2131 and 2819, that added together give a triangular number (4950 = T₉₉).

The spelling of 21312819 in words is "twenty-one million, three hundred twelve thousand, eight hundred nineteen".