20805351691 has 4 divisors (see below), whose sum is σ = 20806470432. Its totient is φ = 20804232952.

The previous prime is 20805351659. The next prime is 20805351701. The reversal of 20805351691 is 19615350802.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19615350802 = 2 ⋅9807675401.

It is a cyclic number.

It is not a de Polignac number, because 20805351691 - 2⁵ = 20805351659 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20805357691) 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, 530995 + ... + 568828.

It is an arithmetic number, because the mean of its divisors is an integer number (5201617608).

Almost surely, 2^20805351691 is an apocalyptic number.

20805351691 is a deficient number, since it is larger than the sum of its proper divisors (1118741).

20805351691 is a wasteful number, since it uses less digits than its factorization.

20805351691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1118740.

The product of its (nonzero) digits is 64800, while the sum is 40.

The spelling of 20805351691 in words is "twenty billion, eight hundred five million, three hundred fifty-one thousand, six hundred ninety-one".