21121215 has 16 divisors (see below), whose sum is σ = 33948288. Its totient is φ = 11213216.

The previous prime is 21121211. The next prime is 21121223. The reversal of 21121215 is 51212112.

It is a cyclic number.

It is not a de Polignac number, because 21121215 - 2² = 21121211 is a prime.

It is a super-2 number, since 2×21121215² = 892211446152450, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a junction number, because it is equal to n+sod(n) for n = 21121194 and 21121203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121211) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 304 + ... + 6506.

It is an arithmetic number, because the mean of its divisors is an integer number (2121768).

Almost surely, 2^21121215 is an apocalyptic number.

21121215 is a deficient number, since it is larger than the sum of its proper divisors (12827073).

21121215 is a wasteful number, since it uses less digits than its factorization.

21121215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6438.

The product of its digits is 40, while the sum is 15.

The square root of 21121215 is about 4595.7823055493. The cubic root of 21121215 is about 276.4222297075.

Adding to 21121215 its reverse (51212112), we get a palindrome (72333327).

The spelling of 21121215 in words is "twenty-one million, one hundred twenty-one thousand, two hundred fifteen".