20021661 has 40 divisors (see below), whose sum is σ = 34081344. Its totient is φ = 11594880.

The previous prime is 20021641. The next prime is 20021663. The reversal of 20021661 is 16612002.

It is a happy number.

20021661 is a `hidden beast` number, since 2 + 0 + 0 + 2 + 1 + 661 = 666.

It is not a de Polignac number, because 20021661 - 2¹⁷ = 19890589 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20021663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 20005 + ... + 20981.

Almost surely, 2^20021661 is an apocalyptic number.

It is an amenable number.

20021661 is a deficient number, since it is larger than the sum of its proper divisors (14059683).

20021661 is a wasteful number, since it uses less digits than its factorization.

20021661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1023 (or 1014 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 20021661 is about 4474.5570730520. The cubic root of 20021661 is about 271.5397213029.

Adding to 20021661 its reverse (16612002), we get a palindrome (36633663).

It can be divided in two parts, 2002 and 1661, that added together give a palindrome (3663).

The spelling of 20021661 in words is "twenty million, twenty-one thousand, six hundred sixty-one".