821672661 has 4 divisors (see below), whose sum is σ = 1095563552. Its totient is φ = 547781772.

The previous prime is 821672633. The next prime is 821672711. The reversal of 821672661 is 166276128.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a de Polignac number, because none of the positive numbers 2^k-821672661 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821672261) 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, 136945441 + ... + 136945446.

It is an arithmetic number, because the mean of its divisors is an integer number (273890888).

Almost surely, 2^821672661 is an apocalyptic number.

It is an amenable number.

821672661 is a deficient number, since it is larger than the sum of its proper divisors (273890891).

821672661 is a wasteful number, since it uses less digits than its factorization.

821672661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 273890890.

The product of its digits is 48384, while the sum is 39.

The square root of 821672661 is about 28664.8331758620. The cubic root of 821672661 is about 936.6261504970.

The spelling of 821672661 in words is "eight hundred twenty-one million, six hundred seventy-two thousand, six hundred sixty-one".