21571517509 has 4 divisors (see below), whose sum is σ = 21692028960. Its totient is φ = 21451006060.

The previous prime is 21571517491. The next prime is 21571517567. The reversal of 21571517509 is 90571517512.

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 21571517509 - 2¹³ = 21571509317 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21571517609) 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, 60255457 + ... + 60255814.

It is an arithmetic number, because the mean of its divisors is an integer number (5423007240).

Almost surely, 2^21571517509 is an apocalyptic number.

It is an amenable number.

21571517509 is a deficient number, since it is larger than the sum of its proper divisors (120511451).

21571517509 is a wasteful number, since it uses less digits than its factorization.

21571517509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 120511450.

The product of its (nonzero) digits is 110250, while the sum is 43.

The spelling of 21571517509 in words is "twenty-one billion, five hundred seventy-one million, five hundred seventeen thousand, five hundred nine".