21000661650 has 72 divisors (see below), whose sum is σ = 57946736484. Its totient is φ = 5448816000.

The previous prime is 21000661631. The next prime is 21000661711. The reversal of 21000661650 is 5616600012.

It is a happy number.

21000661650 is a `hidden beast` number, since 2 + 1 + 0 + 0 + 0 + 6 + 6 + 1 + 650 = 666.

It can be written as a sum of positive squares in 6 ways, for example, as 8740193121 + 12260468529 = 93489^2 + 110727^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 614001 + ... + 647300.

Almost surely, 2^21000661650 is an apocalyptic number.

21000661650 is an abundant number, since it is smaller than the sum of its proper divisors (36946074834).

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

21000661650 is a wasteful number, since it uses less digits than its factorization.

21000661650 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1261356 (or 1261348 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The spelling of 21000661650 in words is "twenty-one billion, six hundred sixty-one thousand, six hundred fifty".