221211991 has 32 divisors (see below), whose sum is σ = 298303488. Its totient is φ = 158423040.

The previous prime is 221211989. The next prime is 221212009. The reversal of 221211991 is 199112122.

It is a cyclic number.

It is not a de Polignac number, because 221211991 - 2¹ = 221211989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221211961) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 383095 + ... + 383671.

It is an arithmetic number, because the mean of its divisors is an integer number (9321984).

Almost surely, 2^221211991 is an apocalyptic number.

221211991 is a deficient number, since it is larger than the sum of its proper divisors (77091497).

221211991 is a wasteful number, since it uses less digits than its factorization.

221211991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 991.

The product of its digits is 648, while the sum is 28.

The square root of 221211991 is about 14873.1970672078. The cubic root of 221211991 is about 604.7876139051.

It can be divided in two parts, 221 and 211991, that added together give a palindrome (212212).

The spelling of 221211991 in words is "two hundred twenty-one million, two hundred eleven thousand, nine hundred ninety-one".