891236721 has 16 divisors (see below), whose sum is σ = 1218264768. Its totient is φ = 579206400.

The previous prime is 891236707. The next prime is 891236777. The reversal of 891236721 is 127632198.

It is not a de Polignac number, because 891236721 - 2¹³ = 891228529 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 891236721.

It is not an unprimeable number, because it can be changed into a prime (891236921) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 227701 + ... + 231581.

It is an arithmetic number, because the mean of its divisors is an integer number (76141548).

Almost surely, 2^891236721 is an apocalyptic number.

It is an amenable number.

891236721 is a deficient number, since it is larger than the sum of its proper divisors (327028047).

891236721 is a wasteful number, since it uses less digits than its factorization.

891236721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5792.

The product of its digits is 36288, while the sum is 39.

The square root of 891236721 is about 29853.5880758076. The cubic root of 891236721 is about 962.3455092682.

The spelling of 891236721 in words is "eight hundred ninety-one million, two hundred thirty-six thousand, seven hundred twenty-one".