221793391 has 4 divisors (see below), whose sum is σ = 221824984. Its totient is φ = 221761800.

The previous prime is 221793379. The next prime is 221793401. The reversal of 221793391 is 193397122.

It is a happy number.

221793391 is a nontrivial binomial coefficient, being equal to C(21062, 2).

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: 193397122 = 2 ⋅96698561.

It is a 3-Lehmer number, since φ(221793391) divides (221793391-1)³.

It is a cyclic number.

It is not a de Polignac number, because 221793391 - 2⁵ = 221793359 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 221793391.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221793361) 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, 1 + ... + 21061.

It is an arithmetic number, because the mean of its divisors is an integer number (55456246).

Almost surely, 2^221793391 is an apocalyptic number.

221793391 is the 21061-st triangular number and also the 10531-st hexagonal number.

221793391 is the 7021-st centered nonagonal number.

221793391 is a deficient number, since it is larger than the sum of its proper divisors (31593).

221793391 is a wasteful number, since it uses less digits than its factorization.

221793391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31592.

The product of its digits is 20412, while the sum is 37.

The square root of 221793391 is about 14892.7294677638. The cubic root of 221793391 is about 605.3169943648.

The spelling of 221793391 in words is "two hundred twenty-one million, seven hundred ninety-three thousand, three hundred ninety-one".