21212779 has 8 divisors (see below), whose sum is σ = 24324608. Its totient is φ = 18121320.

The previous prime is 21212777. The next prime is 21212809. The reversal of 21212779 is 97721212.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21212779 - 2¹ = 21212777 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21212779.

It is not an unprimeable number, because it can be changed into a prime (21212777) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2787 + ... + 7084.

It is an arithmetic number, because the mean of its divisors is an integer number (3040576).

Almost surely, 2^21212779 is an apocalyptic number.

21212779 is a deficient number, since it is larger than the sum of its proper divisors (3111829).

21212779 is an equidigital number, since it uses as much as digits as its factorization.

21212779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10185.

The product of its digits is 3528, while the sum is 31.

The square root of 21212779 is about 4605.7332749520. The cubic root of 21212779 is about 276.8210994071.

It can be divided in two parts, 2121 and 2779, that added together give a square (4900 = 70²).

The spelling of 21212779 in words is "twenty-one million, two hundred twelve thousand, seven hundred seventy-nine".