20688517 has 2 divisors, whose sum is σ = 20688518. Its totient is φ = 20688516.

The previous prime is 20688463. The next prime is 20688529. The reversal of 20688517 is 71588602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19793601 + 894916 = 4449^2 + 946^2 .

It is a cyclic number.

It is not a de Polignac number, because 20688517 - 2¹⁵ = 20655749 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 (20688617) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10344258 + 10344259.

It is an arithmetic number, because the mean of its divisors is an integer number (10344259).

Almost surely, 2^20688517 is an apocalyptic number.

It is an amenable number.

20688517 is a deficient number, since it is larger than the sum of its proper divisors (1).

20688517 is an equidigital number, since it uses as much as digits as its factorization.

20688517 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 26880, while the sum is 37.

The square root of 20688517 is about 4548.4631470421. The cubic root of 20688517 is about 274.5215570720.

It can be divided in two parts, 2068 and 8517, that added together give a triangular number (10585 = T₁₄₅).

The spelling of 20688517 in words is "twenty million, six hundred eighty-eight thousand, five hundred seventeen".