20102561 has 4 divisors (see below), whose sum is σ = 20114052. Its totient is φ = 20091072.

The previous prime is 20102527. The next prime is 20102567. The reversal of 20102561 is 16520102.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 16520102 = 2 ⋅8260051.

It can be written as a sum of positive squares in 2 ways, for example, as 10523536 + 9579025 = 3244^2 + 3095^2 .

It is a cyclic number.

It is not a de Polignac number, because 20102561 - 2⁶ = 20102497 is a prime.

It is a super-2 number, since 2×20102561² = 808225917517442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20102567) 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 3 ways as a sum of consecutive naturals, for example, 2516 + ... + 6821.

It is an arithmetic number, because the mean of its divisors is an integer number (5028513).

Almost surely, 2^20102561 is an apocalyptic number.

It is an amenable number.

20102561 is a deficient number, since it is larger than the sum of its proper divisors (11491).

20102561 is an equidigital number, since it uses as much as digits as its factorization.

20102561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11490.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 20102561 is about 4483.5879605512. The cubic root of 20102561 is about 271.9049597671.

Adding to 20102561 its reverse (16520102), we get a palindrome (36622663).

The spelling of 20102561 in words is "twenty million, one hundred two thousand, five hundred sixty-one".