81615120021 has 128 divisors (see below), whose sum is σ = 134652672000. Its totient is φ = 48643918848.

The previous prime is 81615119959. The next prime is 81615120031. The reversal of 81615120021 is 12002151618.

81615120021 is a `hidden beast` number, since 8 + 1 + 615 + 1 + 20 + 0 + 21 = 666.

It is not a de Polignac number, because 81615120021 - 2¹¹ = 81615117973 is a prime.

It is a super-2 number, since 2×81615120021² (a number of 23 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81615120031) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 126928326 + ... + 126928968.

It is an arithmetic number, because the mean of its divisors is an integer number (1051974000).

Almost surely, 2^81615120021 is an apocalyptic number.

It is an amenable number.

81615120021 is a deficient number, since it is larger than the sum of its proper divisors (53037551979).

81615120021 is a wasteful number, since it uses less digits than its factorization.

81615120021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 880 (or 874 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 27.

Adding to 81615120021 its reverse (12002151618), we get a palindrome (93617271639).

The spelling of 81615120021 in words is "eighty-one billion, six hundred fifteen million, one hundred twenty thousand, twenty-one".