21163631581 has 4 divisors (see below), whose sum is σ = 21171057664. Its totient is φ = 21156205500.

The previous prime is 21163631569. The next prime is 21163631603. The reversal of 21163631581 is 18513636112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21163631581 - 2¹³ = 21163623389 is a prime.

It is a super-2 number, since 2×21163631581² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21163631581.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21163631501) 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, 3708765 + ... + 3714466.

It is an arithmetic number, because the mean of its divisors is an integer number (5292764416).

Almost surely, 2^21163631581 is an apocalyptic number.

It is an amenable number.

21163631581 is a deficient number, since it is larger than the sum of its proper divisors (7426083).

21163631581 is an equidigital number, since it uses as much as digits as its factorization.

21163631581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7426082.

The product of its digits is 25920, while the sum is 37.

The spelling of 21163631581 in words is "twenty-one billion, one hundred sixty-three million, six hundred thirty-one thousand, five hundred eighty-one".