21505415121 has 24 divisors (see below), whose sum is σ = 31667257440. Its totient is φ = 14060753856.

The previous prime is 21505415101. The next prime is 21505415137. The reversal of 21505415121 is 12151450512.

It is a happy number.

21505415121 is a `hidden beast` number, since 2 + 1 + 50 + 541 + 51 + 21 = 666.

It is not a de Polignac number, because 21505415121 - 2¹⁰ = 21505414097 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21505415101) 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, 2731 + ... + 207408.

It is an arithmetic number, because the mean of its divisors is an integer number (1319469060).

Almost surely, 2^21505415121 is an apocalyptic number.

It is an amenable number.

21505415121 is a deficient number, since it is larger than the sum of its proper divisors (10161842319).

21505415121 is a wasteful number, since it uses less digits than its factorization.

21505415121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 210365 (or 210362 counting only the distinct ones).

The product of its (nonzero) digits is 2000, while the sum is 27.

Adding to 21505415121 its reverse (12151450512), we get a palindrome (33656865633).

The spelling of 21505415121 in words is "twenty-one billion, five hundred five million, four hundred fifteen thousand, one hundred twenty-one".