20811521 has 2 divisors, whose sum is σ = 20811522. Its totient is φ = 20811520.

The previous prime is 20811491. The next prime is 20811541. The reversal of 20811521 is 12511802.

It is a happy number.

It is an a-pointer prime, because the next prime (20811541) can be obtained adding 20811521 to its sum of digits (20).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20349121 + 462400 = 4511^2 + 680^2 .

It is a cyclic number.

It is not a de Polignac number, because 20811521 - 2²² = 16617217 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 20811493 and 20811502.

It is not a weakly prime, because it can be changed into another prime (20811541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10405760 + 10405761.

It is an arithmetic number, because the mean of its divisors is an integer number (10405761).

Almost surely, 2^20811521 is an apocalyptic number.

It is an amenable number.

20811521 is a deficient number, since it is larger than the sum of its proper divisors (1).

20811521 is an equidigital number, since it uses as much as digits as its factorization.

20811521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 160, while the sum is 20.

The square root of 20811521 is about 4561.9645987228. The cubic root of 20811521 is about 275.0645402237.

The spelling of 20811521 in words is "twenty million, eight hundred eleven thousand, five hundred twenty-one".