20643281 has 4 divisors (see below), whose sum is σ = 20652864. Its totient is φ = 20633700.

The previous prime is 20643269. The next prime is 20643313. The reversal of 20643281 is 18234602.

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 a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 20643281 - 2¹⁰ = 20642257 is a prime.

It is a super-2 number, since 2×20643281² = 852290100889922, which contains 22 as substring.

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 20643281.

It is not an unprimeable number, because it can be changed into a prime (20643211) 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, 116 + ... + 6426.

It is an arithmetic number, because the mean of its divisors is an integer number (5163216).

Almost surely, 2^20643281 is an apocalyptic number.

It is an amenable number.

20643281 is a deficient number, since it is larger than the sum of its proper divisors (9583).

20643281 is an equidigital number, since it uses as much as digits as its factorization.

20643281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9582.

The product of its (nonzero) digits is 2304, while the sum is 26.

The square root of 20643281 is about 4543.4877572191. The cubic root of 20643281 is about 274.3213281380.

Adding to 20643281 its reverse (18234602), we get a palindrome (38877883).

The spelling of 20643281 in words is "twenty million, six hundred forty-three thousand, two hundred eighty-one".