1645981 has 4 divisors (see below), whose sum is σ = 1661472. Its totient is φ = 1630492.

The previous prime is 1645979. The next prime is 1645999. The reversal of 1645981 is 1895461.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1895461 = 157 ⋅12073.

It is a cyclic number.

It is not a de Polignac number, because 1645981 - 2¹ = 1645979 is a prime.

It is a super-2 number, since 2×1645981² = 5418506904722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1645901) 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, 7585 + ... + 7798.

It is an arithmetic number, because the mean of its divisors is an integer number (415368).

2^1645981 is an apocalyptic number.

It is an amenable number.

1645981 is a deficient number, since it is larger than the sum of its proper divisors (15491).

1645981 is a wasteful number, since it uses less digits than its factorization.

1645981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15490.

The product of its digits is 8640, while the sum is 34.

The square root of 1645981 is about 1282.9579104554. The cubic root of 1645981 is about 118.0705553341.

The spelling of 1645981 in words is "one million, six hundred forty-five thousand, nine hundred eighty-one".