19645981 has 6 divisors (see below), whose sum is σ = 20734782. Its totient is φ = 18611640.

The previous prime is 19645961. The next prime is 19645991. The reversal of 19645981 is 18954691.

It can be written as a sum of positive squares in only one way, i.e., 19096900 + 549081 = 4370^2 + 741^2 .

It is not a de Polignac number, because 19645981 - 2¹³ = 19637789 is a prime.

It is a super-2 number, since 2×19645981² = 771929138904722, 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 (19645961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 26850 + ... + 27571.

It is an arithmetic number, because the mean of its divisors is an integer number (3455797).

Almost surely, 2^19645981 is an apocalyptic number.

It is an amenable number.

19645981 is a deficient number, since it is larger than the sum of its proper divisors (1088801).

19645981 is an equidigital number, since it uses as much as digits as its factorization.

19645981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54459 (or 54440 counting only the distinct ones).

The product of its digits is 77760, while the sum is 43.

The square root of 19645981 is about 4432.3787067443. The cubic root of 19645981 is about 269.8306253670.

The spelling of 19645981 in words is "nineteen million, six hundred forty-five thousand, nine hundred eighty-one".