20865777661 has 4 divisors (see below), whose sum is σ = 20876485500. Its totient is φ = 20855069824.

The previous prime is 20865777659. The next prime is 20865777671. The reversal of 20865777661 is 16677756802.

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

It can be written as a sum of positive squares in 2 ways, for example, as 17467587225 + 3398190436 = 132165^2 + 58294^2 .

It is a cyclic number.

It is not a de Polignac number, because 20865777661 - 2¹ = 20865777659 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20865777671) 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, 5350996 + ... + 5354893.

It is an arithmetic number, because the mean of its divisors is an integer number (5219121375).

Almost surely, 2^20865777661 is an apocalyptic number.

It is an amenable number.

20865777661 is a deficient number, since it is larger than the sum of its proper divisors (10707839).

20865777661 is a wasteful number, since it uses less digits than its factorization.

20865777661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10707838.

The product of its (nonzero) digits is 5927040, while the sum is 55.

The spelling of 20865777661 in words is "twenty billion, eight hundred sixty-five million, seven hundred seventy-seven thousand, six hundred sixty-one".