20021645 has 24 divisors (see below), whose sum is σ = 28366848. Its totient is φ = 13524000.

The previous prime is 20021641. The next prime is 20021663. The reversal of 20021645 is 54612002.

It is a happy number.

It is not a de Polignac number, because 20021645 - 2² = 20021641 is a prime.

It is a super-3 number, since 3×20021645³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

20021645 is a modest number, since divided by 21645 gives 20 as remainder.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20021641) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 16820 + ... + 17970.

It is an arithmetic number, because the mean of its divisors is an integer number (1181952).

Almost surely, 2^20021645 is an apocalyptic number.

It is an amenable number.

20021645 is a deficient number, since it is larger than the sum of its proper divisors (8345203).

20021645 is a wasteful number, since it uses less digits than its factorization.

20021645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1241 (or 1234 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 20021645 is about 4474.5552851652. Note that the first 3 decimals coincide. The cubic root of 20021645 is about 271.5396489706.

Adding to 20021645 its reverse (54612002), we get a palindrome (74633647).

The spelling of 20021645 in words is "twenty million, twenty-one thousand, six hundred forty-five".