1251991 has 8 divisors (see below), whose sum is σ = 1358000. Its totient is φ = 1147392.

The previous prime is 1251983. The next prime is 1252021. The reversal of 1251991 is 1991521.

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 1251991 - 2³ = 1251983 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1251911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2260 + ... + 2758.

It is an arithmetic number, because the mean of its divisors is an integer number (169750).

2^1251991 is an apocalyptic number.

1251991 is a deficient number, since it is larger than the sum of its proper divisors (106009).

1251991 is a wasteful number, since it uses less digits than its factorization.

1251991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 705.

The product of its digits is 810, while the sum is 28.

The square root of 1251991 is about 1118.9240367424. The cubic root of 1251991 is about 107.7788972223.

It can be divided in two parts, 125 and 1991, that added together give a square (2116 = 46²).

The spelling of 1251991 in words is "one million, two hundred fifty-one thousand, nine hundred ninety-one".