21815144531081 has 4 divisors (see below), whose sum is σ = 23798339488464. Its totient is φ = 19831949573700.

The previous prime is 21815144531029. The next prime is 21815144531101. The reversal of 21815144531081 is 18013544151812.

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 not a de Polignac number, because 21815144531081 - 2⁶ = 21815144531017 is a prime.

It is a super-2 number, since 2×21815144531081² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21815144531281) 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, 991597478675 + ... + 991597478696.

It is an arithmetic number, because the mean of its divisors is an integer number (5949584872116).

Almost surely, 2^{21815144531081} is an apocalyptic number.

It is an amenable number.

21815144531081 is a deficient number, since it is larger than the sum of its proper divisors (1983194957383).

21815144531081 is a wasteful number, since it uses less digits than its factorization.

21815144531081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1983194957382.

The product of its (nonzero) digits is 153600, while the sum is 44.

Adding to 21815144531081 its reverse (18013544151812), we get a palindrome (39828688682893).

The spelling of 21815144531081 in words is "twenty-one trillion, eight hundred fifteen billion, one hundred forty-four million, five hundred thirty-one thousand, eighty-one".