20991533 has 2 divisors, whose sum is σ = 20991534. Its totient is φ = 20991532.

The previous prime is 20991527. The next prime is 20991577. The reversal of 20991533 is 33519902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10738729 + 10252804 = 3277^2 + 3202^2 .

It is a cyclic number.

It is not a de Polignac number, because 20991533 - 2⁴ = 20991517 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20991533.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20291533) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495766 + 10495767.

It is an arithmetic number, because the mean of its divisors is an integer number (10495767).

Almost surely, 2^20991533 is an apocalyptic number.

It is an amenable number.

20991533 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991533 is an equidigital number, since it uses as much as digits as its factorization.

20991533 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7290, while the sum is 32.

The square root of 20991533 is about 4581.6517763793. The cubic root of 20991533 is about 275.8553335886.

The spelling of 20991533 in words is "twenty million, nine hundred ninety-one thousand, five hundred thirty-three".