21523695581 has 2 divisors, whose sum is σ = 21523695582. Its totient is φ = 21523695580.

The previous prime is 21523695553. The next prime is 21523695673. The reversal of 21523695581 is 18559632512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21387600025 + 136095556 = 146245^2 + 11666^2 .

It is a cyclic number.

It is not a de Polignac number, because 21523695581 - 2²² = 21519501277 is a prime.

It is a super-3 number, since 3×21523695581³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21523697581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10761847790 + 10761847791.

It is an arithmetic number, because the mean of its divisors is an integer number (10761847791).

Almost surely, 2^21523695581 is an apocalyptic number.

It is an amenable number.

21523695581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523695581 is an equidigital number, since it uses as much as digits as its factorization.

21523695581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 648000, while the sum is 47.

The spelling of 21523695581 in words is "twenty-one billion, five hundred twenty-three million, six hundred ninety-five thousand, five hundred eighty-one".