891209633521 has 3 divisors (see below), whose sum is σ = 891210577561. Its totient is φ = 891208689482.

The previous prime is 891209633519. The next prime is 891209633537. The reversal of 891209633521 is 125336902198.

The square root of 891209633521 is 944039.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 125336902198 = 2 ⋅62668451099.

It is not a de Polignac number, because 891209633521 - 2¹ = 891209633519 is a prime.

It is a super-2 number, since 2×891209633521² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (891209639521) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 472020 + ... + 1416058.

Almost surely, 2^891209633521 is an apocalyptic number.

891209633521 is the 944039-th square number.

891209633521 is the 472020-th centered octagonal number.

It is an amenable number.

891209633521 is a deficient number, since it is larger than the sum of its proper divisors (944040).

891209633521 is an frugal number, since it uses more digits than its factorization.

891209633521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1888078 (or 944039 counting only the distinct ones).

The product of its (nonzero) digits is 699840, while the sum is 49.

Multiplying 891209633521 by its sum of digits (49), we get a square (43669272042529 = 6608273²).

The spelling of 891209633521 in words is "eight hundred ninety-one billion, two hundred nine million, six hundred thirty-three thousand, five hundred twenty-one".