21515405522121 has 24 divisors (see below), whose sum is σ = 35518441033920. Its totient is φ = 12294189909216.

The previous prime is 21515405522081. The next prime is 21515405522123. The reversal of 21515405522121 is 12122550451512.

21515405522121 is a `hidden beast` number, since 2 + 1 + 5 + 1 + 5 + 4 + 0 + 5 + 522 + 121 = 666.

It is not a de Polignac number, because 21515405522121 - 2¹⁰ = 21515405521097 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21515405522123) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2155551 + ... + 6904868.

It is an arithmetic number, because the mean of its divisors is an integer number (1479935043080).

Almost surely, 2^{21515405522121} is an apocalyptic number.

21515405522121 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21515405522121 is a deficient number, since it is larger than the sum of its proper divisors (14003035511799).

21515405522121 is a wasteful number, since it uses less digits than its factorization.

21515405522121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9098125 (or 9098122 counting only the distinct ones).

The product of its (nonzero) digits is 40000, while the sum is 36.

Adding to 21515405522121 its reverse (12122550451512), we get a palindrome (33637955973633).

The spelling of 21515405522121 in words is "twenty-one trillion, five hundred fifteen billion, four hundred five million, five hundred twenty-two thousand, one hundred twenty-one".