211221991 has 8 divisors (see below), whose sum is σ = 225074160. Its totient is φ = 197528448.

The previous prime is 211221979. The next prime is 211222019. The reversal of 211221991 is 199122112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 211221991 - 2¹⁹ = 210697703 is a prime.

It is a super-2 number, since 2×211221991² = 89229458964008162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (211221931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 36901 + ... + 42238.

It is an arithmetic number, because the mean of its divisors is an integer number (28134270).

Almost surely, 2^211221991 is an apocalyptic number.

211221991 is a deficient number, since it is larger than the sum of its proper divisors (13852169).

211221991 is a wasteful number, since it uses less digits than its factorization.

211221991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 79313.

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

The square root of 211221991 is about 14533.4782829163. The cubic root of 211221991 is about 595.5428898600.

It can be divided in two parts, 211221 and 991, that added together give a palindrome (212212).

The spelling of 211221991 in words is "two hundred eleven million, two hundred twenty-one thousand, nine hundred ninety-one".