212121 has 36 divisors (see below), whose sum is σ = 394212. Its totient is φ = 108864.

The previous prime is 212117. The next prime is 212123. The reversal of 212121 is 121212.

212121 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.

It can be written as a sum of positive squares in 2 ways, for example, as 112896 + 99225 = 336^2 + 315^2 .

It is not a de Polignac number, because 212121 - 2² = 212117 is a prime.

It is a super-3 number, since 3×212121³ = 28633355956342683, which contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (9).

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

212121 is an undulating number in base 10.

212121 is a modest number, since divided by 2121 gives 21 as remainder.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (212123) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 5715 + ... + 5751.

2²¹²¹²¹ is an apocalyptic number.

212121 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

212121 is a deficient number, since it is larger than the sum of its proper divisors (182091).

212121 is a wasteful number, since it uses less digits than its factorization.

212121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70 (or 60 counting only the distinct ones).

The product of its digits is 8, while the sum is 9.

The square root of 212121 is about 460.5659561887. The cubic root of 212121 is about 59.6386616112.

Adding to 212121 its reverse (121212), we get a palindrome (333333).

Subtracting from 212121 its reverse (121212), we obtain a palindrome (90909).

It can be divided in two parts, 212 and 121, that multiplied together give a palindrome (25652).

The spelling of 212121 in words is "two hundred twelve thousand, one hundred twenty-one", and thus it is an iban number.