21131993 has 4 divisors (see below), whose sum is σ = 21239460. Its totient is φ = 21024528.

The previous prime is 21131989. The next prime is 21132011. The reversal of 21131993 is 39913112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 9653449 + 11478544 = 3107^2 + 3388^2 .

It is a cyclic number.

It is not a de Polignac number, because 21131993 - 2² = 21131989 is a prime.

It is a super-2 number, since 2×21131993² = 893122256304098, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21131983) 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, 53438 + ... + 53831.

It is an arithmetic number, because the mean of its divisors is an integer number (5309865).

Almost surely, 2^21131993 is an apocalyptic number.

It is an amenable number.

21131993 is a deficient number, since it is larger than the sum of its proper divisors (107467).

21131993 is a wasteful number, since it uses less digits than its factorization.

21131993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 107466.

The product of its digits is 1458, while the sum is 29.

The square root of 21131993 is about 4596.9547528772. The cubic root of 21131993 is about 276.4692404527.

The spelling of 21131993 in words is "twenty-one million, one hundred thirty-one thousand, nine hundred ninety-three".