21686090651 has 4 divisors (see below), whose sum is σ = 21687226704. Its totient is φ = 21684954600.

The previous prime is 21686090611. The next prime is 21686090677. The reversal of 21686090651 is 15609068612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21686090651 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21686090611) 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, 538895 + ... + 577736.

It is an arithmetic number, because the mean of its divisors is an integer number (5421806676).

Almost surely, 2^21686090651 is an apocalyptic number.

21686090651 is a deficient number, since it is larger than the sum of its proper divisors (1136053).

21686090651 is a wasteful number, since it uses less digits than its factorization.

21686090651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1136052.

The product of its (nonzero) digits is 155520, while the sum is 44.

The spelling of 21686090651 in words is "twenty-one billion, six hundred eighty-six million, ninety thousand, six hundred fifty-one".