20971521 has 16 divisors (see below), whose sum is σ = 31374720. Its totient is φ = 13843440.

The previous prime is 20971507. The next prime is 20971529. The reversal of 20971521 is 12517902.

It is a Cullen number, since it is equal to 20×2²⁰+1.

It is a de Polignac number, because none of the positive numbers 2^k-20971521 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (20971529) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 990 + ... + 6551.

It is an arithmetic number, because the mean of its divisors is an integer number (1960920).

It is a Proth number, since it is equal to 5 ⋅ 2²² + 1 and 5 < 2²².

Almost surely, 2^20971521 is an apocalyptic number.

It is an amenable number.

20971521 is a deficient number, since it is larger than the sum of its proper divisors (10403199).

20971521 is a wasteful number, since it uses less digits than its factorization.

20971521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7653 (or 7647 counting only the distinct ones).

The product of its (nonzero) digits is 1260, while the sum is 27.

The square root of 20971521 is about 4579.4673271026. The cubic root of 20971521 is about 275.7676447073.

The spelling of 20971521 in words is "twenty million, nine hundred seventy-one thousand, five hundred twenty-one".