78999921 has 128 divisors (see below), whose sum is σ = 163430400. Its totient is φ = 36391680.

The previous prime is 78999913. The next prime is 78999923. The reversal of 78999921 is 12999987.

It is not a de Polignac number, because 78999921 - 2³ = 78999913 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78999923) 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, 999960 + ... + 1000038.

It is an arithmetic number, because the mean of its divisors is an integer number (1276800).

Almost surely, 2^78999921 is an apocalyptic number.

It is an amenable number.

78999921 is an abundant number, since it is smaller than the sum of its proper divisors (84430479).

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

78999921 is a wasteful number, since it uses less digits than its factorization.

78999921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 156 (or 150 counting only the distinct ones).

The product of its digits is 734832, while the sum is 54.

The square root of 78999921 is about 8888.1899732173. The cubic root of 78999921 is about 429.0838996746.

It can be divided in two parts, 78 and 999921, that added together give a palindrome (999999).

The spelling of 78999921 in words is "seventy-eight million, nine hundred ninety-nine thousand, nine hundred twenty-one".