20556521 has 2 divisors, whose sum is σ = 20556522. Its totient is φ = 20556520.

The previous prime is 20556517. The next prime is 20556533. The reversal of 20556521 is 12565502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18800896 + 1755625 = 4336^2 + 1325^2 .

It is a cyclic number.

It is not a de Polignac number, because 20556521 - 2² = 20556517 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (20556541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10278260 + 10278261.

It is an arithmetic number, because the mean of its divisors is an integer number (10278261).

Almost surely, 2^20556521 is an apocalyptic number.

It is an amenable number.

20556521 is a deficient number, since it is larger than the sum of its proper divisors (1).

20556521 is an equidigital number, since it uses as much as digits as its factorization.

20556521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3000, while the sum is 26.

The square root of 20556521 is about 4533.9299729925. The cubic root of 20556521 is about 273.9364807383.

The spelling of 20556521 in words is "twenty million, five hundred fifty-six thousand, five hundred twenty-one".