21212780 has 24 divisors (see below), whose sum is σ = 44731008. Its totient is φ = 8450048.

The previous prime is 21212777. The next prime is 21212809. The reversal of 21212780 is 8721212.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3077 + ... + 7203.

It is an arithmetic number, because the mean of its divisors is an integer number (1863792).

Almost surely, 2^21212780 is an apocalyptic number.

21212780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21212780 is an abundant number, since it is smaller than the sum of its proper divisors (23518228).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21212780 is a wasteful number, since it uses less digits than its factorization.

21212780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4393 (or 4391 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 21212780 is about 4605.7333835123. The cubic root of 21212780 is about 276.8211037570.

Adding to 21212780 its reverse (8721212), we get a palindrome (29933992).

The spelling of 21212780 in words is "twenty-one million, two hundred twelve thousand, seven hundred eighty".