21210121 has 4 divisors (see below), whose sum is σ = 21320212. Its totient is φ = 21100032.

The previous prime is 21210109. The next prime is 21210151. The reversal of 21210121 is 12101212.

21210121 = T₃₆₉ + T₃₇₀ + ... + T₅₆₁.

21210121 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4888521 + 16321600 = 2211^2 + 4040^2 .

It is a cyclic number.

It is not a de Polignac number, because 21210121 - 2⁵ = 21210089 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21210098 and 21210107.

It is not an unprimeable number, because it can be changed into a prime (21210151) 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, 54756 + ... + 55141.

It is an arithmetic number, because the mean of its divisors is an integer number (5330053).

Almost surely, 2^21210121 is an apocalyptic number.

It is an amenable number.

21210121 is a deficient number, since it is larger than the sum of its proper divisors (110091).

21210121 is a wasteful number, since it uses less digits than its factorization.

21210121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110090.

The product of its (nonzero) digits is 8, while the sum is 10.

The square root of 21210121 is about 4605.4447125115. Note that the first 3 decimals coincide. The cubic root of 21210121 is about 276.8095368608.

Adding to 21210121 its reverse (12101212), we get a palindrome (33311333).

It can be divided in two parts, 2 and 1210121, that multiplied together give a palindrome (2420242).

The spelling of 21210121 in words is "twenty-one million, two hundred ten thousand, one hundred twenty-one".