20678521 has 4 divisors (see below), whose sum is σ = 20841472. Its totient is φ = 20515572.

The previous prime is 20678513. The next prime is 20678531. The reversal of 20678521 is 12587602.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12587602 = 2 ⋅6293801.

It is a cyclic number.

It is not a de Polignac number, because 20678521 - 2³ = 20678513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20678531) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 81285 + ... + 81538.

It is an arithmetic number, because the mean of its divisors is an integer number (5210368).

Almost surely, 2^20678521 is an apocalyptic number.

It is an amenable number.

20678521 is a deficient number, since it is larger than the sum of its proper divisors (162951).

20678521 is a wasteful number, since it uses less digits than its factorization.

20678521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 162950.

The product of its (nonzero) digits is 6720, while the sum is 31.

The square root of 20678521 is about 4547.3641815892. The cubic root of 20678521 is about 274.4773367354.

The spelling of 20678521 in words is "twenty million, six hundred seventy-eight thousand, five hundred twenty-one".