21378661812 has 72 divisors (see below), whose sum is σ = 55827699200. Its totient is φ = 6890909760.

The previous prime is 21378661789. The next prime is 21378661853. The reversal of 21378661812 is 21816687312.

21378661812 is a `hidden beast` number, since 2 + 13 + 7 + 8 + 6 + 618 + 12 = 666.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1554438 + ... + 1568130.

Almost surely, 2^21378661812 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21378661812, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27913849600).

21378661812 is an abundant number, since it is smaller than the sum of its proper divisors (34449037388).

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

21378661812 is a wasteful number, since it uses less digits than its factorization.

21378661812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15133 (or 15128 counting only the distinct ones).

The product of its digits is 193536, while the sum is 45.

The spelling of 21378661812 in words is "twenty-one billion, three hundred seventy-eight million, six hundred sixty-one thousand, eight hundred twelve".