20571561 has 12 divisors (see below), whose sum is σ = 29894592. Its totient is φ = 13631256.

The previous prime is 20571557. The next prime is 20571599. The reversal of 20571561 is 16517502.

It is not a de Polignac number, because 20571561 - 2² = 20571557 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20571511) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5341 + ... + 8346.

It is an arithmetic number, because the mean of its divisors is an integer number (2491216).

Almost surely, 2^20571561 is an apocalyptic number.

It is an amenable number.

20571561 is a deficient number, since it is larger than the sum of its proper divisors (9323031).

20571561 is a wasteful number, since it uses less digits than its factorization.

20571561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13860 (or 13857 counting only the distinct ones).

The product of its (nonzero) digits is 2100, while the sum is 27.

The square root of 20571561 is about 4535.5882749650. The cubic root of 20571561 is about 274.0032722006.

The spelling of 20571561 in words is "twenty million, five hundred seventy-one thousand, five hundred sixty-one".