8421805661 has 8 divisors (see below), whose sum is σ = 8926739640. Its totient is φ = 7917931008.

The previous prime is 8421805643. The next prime is 8421805709. The reversal of 8421805661 is 1665081248.

It can be written as a sum of positive squares in 4 ways, for example, as 1331155225 + 7090650436 = 36485^2 + 84206^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 8421805661 - 2¹⁸ = 8421543517 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 (8421805621) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 248426 + ... + 280283.

It is an arithmetic number, because the mean of its divisors is an integer number (1115842455).

Almost surely, 2^8421805661 is an apocalyptic number.

It is an amenable number.

8421805661 is a deficient number, since it is larger than the sum of its proper divisors (504933979).

8421805661 is a wasteful number, since it uses less digits than its factorization.

8421805661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 529663.

The product of its (nonzero) digits is 92160, while the sum is 41.

The square root of 8421805661 is about 91770.3964304394. The cubic root of 8421805661 is about 2034.5501774478.

The spelling of 8421805661 in words is "eight billion, four hundred twenty-one million, eight hundred five thousand, six hundred sixty-one".