21515816387 has 32 divisors (see below), whose sum is σ = 24766089600. Its totient is φ = 18655588224.

The previous prime is 21515816351. The next prime is 21515816401. The reversal of 21515816387 is 78361851512.

It is a de Polignac number, because none of the positive numbers 2^k-21515816387 is a prime.

It is a super-3 number, since 3×21515816387³ (a number of 32 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21515816317) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2352818 + ... + 2361944.

It is an arithmetic number, because the mean of its divisors is an integer number (773940300).

Almost surely, 2^21515816387 is an apocalyptic number.

21515816387 is a deficient number, since it is larger than the sum of its proper divisors (3250273213).

21515816387 is an equidigital number, since it uses as much as digits as its factorization.

21515816387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9232 (or 9206 counting only the distinct ones).

The product of its digits is 403200, while the sum is 47.

The spelling of 21515816387 in words is "twenty-one billion, five hundred fifteen million, eight hundred sixteen thousand, three hundred eighty-seven".