21565657819 has 4 divisors (see below), whose sum is σ = 22834225944. Its totient is φ = 20297089696.

The previous prime is 21565657741. The next prime is 21565657823. The reversal of 21565657819 is 91875656512.

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

It is a cyclic number.

It is not a de Polignac number, because 21565657819 - 2⁹ = 21565657307 is a prime.

It is a super-2 number, since 2×21565657819² (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 21565657819.

It is not an unprimeable number, because it can be changed into a prime (21565657859) 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, 634284037 + ... + 634284070.

It is an arithmetic number, because the mean of its divisors is an integer number (5708556486).

Almost surely, 2^21565657819 is an apocalyptic number.

21565657819 is a deficient number, since it is larger than the sum of its proper divisors (1268568125).

21565657819 is a wasteful number, since it uses less digits than its factorization.

21565657819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1268568124.

The product of its digits is 4536000, while the sum is 55.

The spelling of 21565657819 in words is "twenty-one billion, five hundred sixty-five million, six hundred fifty-seven thousand, eight hundred nineteen".