20957561 has 2 divisors, whose sum is σ = 20957562. Its totient is φ = 20957560.

The previous prime is 20957537. The next prime is 20957593. The reversal of 20957561 is 16575902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20839225 + 118336 = 4565^2 + 344^2 .

It is a cyclic number.

It is not a de Polignac number, because 20957561 - 2¹⁴ = 20941177 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (20957161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10478780 + 10478781.

It is an arithmetic number, because the mean of its divisors is an integer number (10478781).

Almost surely, 2^20957561 is an apocalyptic number.

It is an amenable number.

20957561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20957561 is an equidigital number, since it uses as much as digits as its factorization.

20957561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 18900, while the sum is 35.

The square root of 20957561 is about 4577.9428786301. The cubic root of 20957561 is about 275.7064415349.

The spelling of 20957561 in words is "twenty million, nine hundred fifty-seven thousand, five hundred sixty-one".