20778517 has 2 divisors, whose sum is σ = 20778518. Its totient is φ = 20778516.

The previous prime is 20778493. The next prime is 20778521. The reversal of 20778517 is 71587702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20738916 + 39601 = 4554^2 + 199^2 .

It is a cyclic number.

It is not a de Polignac number, because 20778517 - 2⁷ = 20778389 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20778557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10389258 + 10389259.

It is an arithmetic number, because the mean of its divisors is an integer number (10389259).

Almost surely, 2^20778517 is an apocalyptic number.

It is an amenable number.

20778517 is a deficient number, since it is larger than the sum of its proper divisors (1).

20778517 is an equidigital number, since it uses as much as digits as its factorization.

20778517 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 27440, while the sum is 37.

The square root of 20778517 is about 4558.3458622619. The cubic root of 20778517 is about 274.9190593747.

The spelling of 20778517 in words is "twenty million, seven hundred seventy-eight thousand, five hundred seventeen".