21510509991 has 8 divisors (see below), whose sum is σ = 28682295024. Its totient is φ = 14339532480.

The previous prime is 21510509963. The next prime is 21510510029. The reversal of 21510509991 is 19990501512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21510509991 - 2¹⁵ = 21510477223 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21510509941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 136720 + ... + 248421.

It is an arithmetic number, because the mean of its divisors is an integer number (3585286878).

Almost surely, 2^21510509991 is an apocalyptic number.

21510509991 is a deficient number, since it is larger than the sum of its proper divisors (7171785033).

21510509991 is a wasteful number, since it uses less digits than its factorization.

21510509991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 403761.

The product of its (nonzero) digits is 36450, while the sum is 42.

The spelling of 21510509991 in words is "twenty-one billion, five hundred ten million, five hundred nine thousand, nine hundred ninety-one".