20991577 has 2 divisors, whose sum is σ = 20991578. Its totient is φ = 20991576.

The previous prime is 20991533. The next prime is 20991601. The reversal of 20991577 is 77519902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20967241 + 24336 = 4579^2 + 156^2 .

It is a cyclic number.

It is not a de Polignac number, because 20991577 - 2¹⁵ = 20958809 is a prime.

It is not a weakly prime, because it can be changed into another prime (20991517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495788 + 10495789.

It is an arithmetic number, because the mean of its divisors is an integer number (10495789).

Almost surely, 2^20991577 is an apocalyptic number.

It is an amenable number.

20991577 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991577 is an equidigital number, since it uses as much as digits as its factorization.

20991577 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 39690, while the sum is 40.

The square root of 20991577 is about 4581.6565781385. The cubic root of 20991577 is about 275.8555263270.

The spelling of 20991577 in words is "twenty million, nine hundred ninety-one thousand, five hundred seventy-seven".