20642561 has 2 divisors, whose sum is σ = 20642562. Its totient is φ = 20642560.

The previous prime is 20642527. The next prime is 20642563. The reversal of 20642561 is 16524602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13249600 + 7392961 = 3640^2 + 2719^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20642561 is a prime.

It is a super-2 number, since 2×20642561² = 852230649277442, which contains 22 as substring.

Together with 20642563, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20642561.

It is not a weakly prime, because it can be changed into another prime (20642563) 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 as a sum of consecutive naturals, namely, 10321280 + 10321281.

It is an arithmetic number, because the mean of its divisors is an integer number (10321281).

Almost surely, 2^20642561 is an apocalyptic number.

It is an amenable number.

20642561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20642561 is an equidigital number, since it uses as much as digits as its factorization.

20642561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2880, while the sum is 26.

The square root of 20642561 is about 4543.4085222441. The cubic root of 20642561 is about 274.3181388250.

The spelling of 20642561 in words is "twenty million, six hundred forty-two thousand, five hundred sixty-one".