21987511287878 has 8 divisors (see below), whose sum is σ = 34921341457272. Its totient is φ = 10347064135456.

The previous prime is 21987511287877. The next prime is 21987511287893. The reversal of 21987511287878 is 87878211578912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987511287877) 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, 323345754200 + ... + 323345754267.

It is an arithmetic number, because the mean of its divisors is an integer number (4365167682159).

Almost surely, 2^{21987511287878} is an apocalyptic number.

21987511287878 is a deficient number, since it is larger than the sum of its proper divisors (12933830169394).

21987511287878 is a wasteful number, since it uses less digits than its factorization.

21987511287878 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 646691508486.

The product of its digits is 252887040, while the sum is 74.

The spelling of 21987511287878 in words is "twenty-one trillion, nine hundred eighty-seven billion, five hundred eleven million, two hundred eighty-seven thousand, eight hundred seventy-eight".