1621691 has 4 divisors (see below), whose sum is σ = 1624584. Its totient is φ = 1618800.

The previous prime is 1621679. The next prime is 1621699. The reversal of 1621691 is 1961261.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1961261 = 127 ⋅15443.

It is a cyclic number.

It is not a de Polignac number, because 1621691 - 2¹⁰ = 1620667 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1621691.

It is not an unprimeable number, because it can be changed into a prime (1621699) 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, 305 + ... + 1826.

It is an arithmetic number, because the mean of its divisors is an integer number (406146).

2^1621691 is an apocalyptic number.

1621691 is a deficient number, since it is larger than the sum of its proper divisors (2893).

1621691 is an equidigital number, since it uses as much as digits as its factorization.

1621691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2892.

The product of its digits is 648, while the sum is 26.

The square root of 1621691 is about 1273.4563204131. The cubic root of 1621691 is about 117.4868794766.

The spelling of 1621691 in words is "one million, six hundred twenty-one thousand, six hundred ninety-one".