20715521 has 4 divisors (see below), whose sum is σ = 20909232.
Its totient is φ = 20521812.
The previous prime is 20715517. The next prime is 20715547. The reversal of 20715521 is 12551702.
It is a happy number.
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.
It is a cyclic number.
It is not a de Polignac number, because 20715521 - 22 = 20715517 is a prime.
It is a Duffinian number.
It is a Curzon number.
It is not an unprimeable number, because it can be changed into a prime (20715581) 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, 96695 + ... + 96908.
It is an arithmetic number, because the mean of its divisors is an integer number (5227308).
Almost surely, 220715521 is an apocalyptic number.
It is an amenable number.
20715521 is a deficient number, since it is larger than the sum of its proper divisors (193711).
20715521 is a wasteful number, since it uses less digits than its factorization.
20715521 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 193710.
The product of its (nonzero) digits is 700, while the sum is 23.
The square root of 20715521 is about 4551.4306542009.
The cubic root of 20715521 is about 274.6409462816.
The spelling of 20715521 in words is "twenty million, seven hundred fifteen thousand, five hundred twenty-one".