861921661 has 4 divisors (see below), whose sum is σ = 862462972. Its totient is φ = 861380352.

The previous prime is 861921659. The next prime is 861921677. The reversal of 861921661 is 166129168.

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 215796100 + 646125561 = 14690^2 + 25419^2 .

It is a cyclic number.

It is not a de Polignac number, because 861921661 - 2¹ = 861921659 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 (861921631) 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, 268260 + ... + 271453.

It is an arithmetic number, because the mean of its divisors is an integer number (215615743).

Almost surely, 2^861921661 is an apocalyptic number.

It is an amenable number.

861921661 is a deficient number, since it is larger than the sum of its proper divisors (541311).

861921661 is a wasteful number, since it uses less digits than its factorization.

861921661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 541310.

The product of its digits is 31104, while the sum is 40.

The square root of 861921661 is about 29358.5023630294. The cubic root of 861921661 is about 951.6763241407.

The spelling of 861921661 in words is "eight hundred sixty-one million, nine hundred twenty-one thousand, six hundred sixty-one".