21506550651 has 20 divisors (see below), whose sum is σ = 32134685352. Its totient is φ = 14334301728.

The previous prime is 21506550647. The next prime is 21506550671. The reversal of 21506550651 is 15605560512.

21506550651 is a `hidden beast` number, since 2 + 1 + 50 + 6 + 550 + 6 + 51 = 666.

It is not a de Polignac number, because 21506550651 - 2² = 21506550647 is a prime.

It is a super-3 number, since 3×21506550651³ (a number of 32 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (21506550671) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 339111 + ... + 397503.

Almost surely, 2^21506550651 is an apocalyptic number.

21506550651 is a deficient number, since it is larger than the sum of its proper divisors (10628134701).

21506550651 is an equidigital number, since it uses as much as digits as its factorization.

21506550651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62952 (or 62943 counting only the distinct ones).

The product of its (nonzero) digits is 45000, while the sum is 36.

The spelling of 21506550651 in words is "twenty-one billion, five hundred six million, five hundred fifty thousand, six hundred fifty-one".