21288651978 has 16 divisors (see below), whose sum is σ = 46447968096. Its totient is φ = 6451106640.

The previous prime is 21288651977. The next prime is 21288652019. The reversal of 21288651978 is 87915688212.

It is not an unprimeable number, because it can be changed into a prime (21288651977) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 161277601 + ... + 161277732.

It is an arithmetic number, because the mean of its divisors is an integer number (2902998006).

Almost surely, 2^21288651978 is an apocalyptic number.

21288651978 is an abundant number, since it is smaller than the sum of its proper divisors (25159316118).

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

21288651978 is a wasteful number, since it uses less digits than its factorization.

21288651978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 322555349.

The product of its digits is 3870720, while the sum is 57.

The spelling of 21288651978 in words is "twenty-one billion, two hundred eighty-eight million, six hundred fifty-one thousand, nine hundred seventy-eight".