1620991 has 4 divisors (see below), whose sum is σ = 1625184. Its totient is φ = 1616800.

The previous prime is 1620989. The next prime is 1621019. The reversal of 1620991 is 1990261.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1620991 - 2¹ = 1620989 is a prime.

It is a super-2 number, since 2×1620991² = 5255223644162, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1620961) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1450 + ... + 2311.

It is an arithmetic number, because the mean of its divisors is an integer number (406296).

2^1620991 is an apocalyptic number.

1620991 is a deficient number, since it is larger than the sum of its proper divisors (4193).

1620991 is an equidigital number, since it uses as much as digits as its factorization.

1620991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4192.

The product of its (nonzero) digits is 972, while the sum is 28.

The square root of 1620991 is about 1273.1814481840. The cubic root of 1620991 is about 117.4699727104.

The spelling of 1620991 in words is "one million, six hundred twenty thousand, nine hundred ninety-one".