21166897815 has 96 divisors (see below), whose sum is σ = 43944975360. Its totient is φ = 9215129088.

The previous prime is 21166897811. The next prime is 21166897819. The reversal of 21166897815 is 51879866112.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21166897811) and next prime (21166897819).

It is not a de Polignac number, because 21166897815 - 2² = 21166897811 is a prime.

It is a super-2 number, since 2×21166897815² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21166897811) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 1681816 + ... + 1694354.

It is an arithmetic number, because the mean of its divisors is an integer number (457760160).

Almost surely, 2^21166897815 is an apocalyptic number.

21166897815 is an abundant number, since it is smaller than the sum of its proper divisors (22778077545).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21166897815 is a wasteful number, since it uses less digits than its factorization.

21166897815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12813 (or 12810 counting only the distinct ones).

The product of its digits is 1451520, while the sum is 54.

The spelling of 21166897815 in words is "twenty-one billion, one hundred sixty-six million, eight hundred ninety-seven thousand, eight hundred fifteen".