21516121 has 4 divisors (see below), whose sum is σ = 23472144. Its totient is φ = 19560100.

The previous prime is 21516119. The next prime is 21516127. The reversal of 21516121 is 12161512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21516121 - 2¹ = 21516119 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21516127) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 977995 + ... + 978016.

It is an arithmetic number, because the mean of its divisors is an integer number (5868036).

Almost surely, 2^21516121 is an apocalyptic number.

It is an amenable number.

21516121 is a deficient number, since it is larger than the sum of its proper divisors (1956023).

21516121 is a wasteful number, since it uses less digits than its factorization.

21516121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1956022.

The product of its digits is 120, while the sum is 19.

The square root of 21516121 is about 4638.5472941429. The cubic root of 21516121 is about 278.1343699406.

Adding to 21516121 its reverse (12161512), we get a palindrome (33677633).

The spelling of 21516121 in words is "twenty-one million, five hundred sixteen thousand, one hundred twenty-one".