1221891 has 16 divisors (see below), whose sum is σ = 1809408. Its totient is φ = 727200.

The previous prime is 1221863. The next prime is 1221907. The reversal of 1221891 is 1981221.

It is not a de Polignac number, because 1221891 - 2⁹ = 1221379 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1221811) 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, 1710 + ... + 2316.

It is an arithmetic number, because the mean of its divisors is an integer number (113088).

2^1221891 is an apocalyptic number.

1221891 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

1221891 is a deficient number, since it is larger than the sum of its proper divisors (587517).

1221891 is a wasteful number, since it uses less digits than its factorization.

1221891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 682.

The product of its digits is 288, while the sum is 24.

The square root of 1221891 is about 1105.3917857484. The cubic root of 1221891 is about 106.9081518850.

It can be divided in two parts, 1221 and 891, that added together give a palindrome (2112).

The spelling of 1221891 in words is "one million, two hundred twenty-one thousand, eight hundred ninety-one".