20643257 has 2 divisors, whose sum is σ = 20643258. Its totient is φ = 20643256.

The previous prime is 20643251. The next prime is 20643269. The reversal of 20643257 is 75234602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20394256 + 249001 = 4516^2 + 499^2 .

It is a cyclic number.

It is not a de Polignac number, because 20643257 - 2¹⁶ = 20577721 is a prime.

It is a super-2 number, since 2×20643257² = 852288119136098, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20643251) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10321628 + 10321629.

It is an arithmetic number, because the mean of its divisors is an integer number (10321629).

Almost surely, 2^20643257 is an apocalyptic number.

It is an amenable number.

20643257 is a deficient number, since it is larger than the sum of its proper divisors (1).

20643257 is an equidigital number, since it uses as much as digits as its factorization.

20643257 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10080, while the sum is 29.

The square root of 20643257 is about 4543.4851160755. The cubic root of 20643257 is about 274.3212218288.

Adding to 20643257 its reverse (75234602), we get a palindrome (95877859).

The spelling of 20643257 in words is "twenty million, six hundred forty-three thousand, two hundred fifty-seven".