20491561 has 2 divisors, whose sum is σ = 20491562. Its totient is φ = 20491560.

The previous prime is 20491489. The next prime is 20491567. The reversal of 20491561 is 16519402.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18147600 + 2343961 = 4260^2 + 1531^2 .

It is a cyclic number.

It is not a de Polignac number, because 20491561 - 2⁷ = 20491433 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20491567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10245780 + 10245781.

It is an arithmetic number, because the mean of its divisors is an integer number (10245781).

Almost surely, 2^20491561 is an apocalyptic number.

It is an amenable number.

20491561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20491561 is an equidigital number, since it uses as much as digits as its factorization.

20491561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 20491561 is about 4526.7605414910. The cubic root of 20491561 is about 273.6476236381.

The spelling of 20491561 in words is "twenty million, four hundred ninety-one thousand, five hundred sixty-one".