21581990513 has 4 divisors (see below), whose sum is σ = 21650072820. Its totient is φ = 21513908208.

The previous prime is 21581990509. The next prime is 21581990519. The reversal of 21581990513 is 31509918512.

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 8702464369 + 12879526144 = 93287^2 + 113488^2 .

It is a cyclic number.

It is not a de Polignac number, because 21581990513 - 2² = 21581990509 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21581990519) 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, 34040678 + ... + 34041311.

It is an arithmetic number, because the mean of its divisors is an integer number (5412518205).

Almost surely, 2^21581990513 is an apocalyptic number.

It is an amenable number.

21581990513 is a deficient number, since it is larger than the sum of its proper divisors (68082307).

21581990513 is an equidigital number, since it uses as much as digits as its factorization.

21581990513 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 68082306.

The product of its (nonzero) digits is 97200, while the sum is 44.

The spelling of 21581990513 in words is "twenty-one billion, five hundred eighty-one million, nine hundred ninety thousand, five hundred thirteen".