1521991 has 2 divisors, whose sum is σ = 1521992. Its totient is φ = 1521990.

The previous prime is 1521983. The next prime is 1522009. The reversal of 1521991 is 1991251.

It is a weak prime.

It is an emirp because it is prime and its reverse (1991251) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1521991 - 2³ = 1521983 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1521901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 760995 + 760996.

It is an arithmetic number, because the mean of its divisors is an integer number (760996).

2^1521991 is an apocalyptic number.

1521991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1521991 is an equidigital number, since it uses as much as digits as its factorization.

1521991 is an evil number, because the sum of its binary digits is even.

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

The square root of 1521991 is about 1233.6899934749. The cubic root of 1521991 is about 115.0281216671.

The spelling of 1521991 in words is "one million, five hundred twenty-one thousand, nine hundred ninety-one".