21115721571 has 16 divisors (see below), whose sum is σ = 32223469824. Its totient is φ = 12048452064.

The previous prime is 21115721569. The next prime is 21115721581. The reversal of 21115721571 is 17512751112.

It is not a de Polignac number, because 21115721571 - 2¹ = 21115721569 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21115721521) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 721756 + ... + 750441.

It is an arithmetic number, because the mean of its divisors is an integer number (2013966864).

Almost surely, 2^21115721571 is an apocalyptic number.

21115721571 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21115721571 is a deficient number, since it is larger than the sum of its proper divisors (11107748253).

21115721571 is a wasteful number, since it uses less digits than its factorization.

21115721571 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1472890.

The product of its digits is 4900, while the sum is 33.

The spelling of 21115721571 in words is "twenty-one billion, one hundred fifteen million, seven hundred twenty-one thousand, five hundred seventy-one".