21218077 has 4 divisors (see below), whose sum is σ = 21246300. Its totient is φ = 21189856.

The previous prime is 21218069. The next prime is 21218083. The reversal of 21218077 is 77081212.

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 7778521 + 13439556 = 2789^2 + 3666^2 .

It is a cyclic number.

It is not a de Polignac number, because 21218077 - 2³ = 21218069 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218777) 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, 12952 + ... + 14497.

It is an arithmetic number, because the mean of its divisors is an integer number (5311575).

Almost surely, 2^21218077 is an apocalyptic number.

It is an amenable number.

21218077 is a deficient number, since it is larger than the sum of its proper divisors (28223).

21218077 is an equidigital number, since it uses as much as digits as its factorization.

21218077 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28222.

The product of its (nonzero) digits is 1568, while the sum is 28.

The square root of 21218077 is about 4606.3083917602. The cubic root of 21218077 is about 276.8441433170.

Adding to 21218077 its reverse (77081212), we get a palindrome (98299289).

The spelling of 21218077 in words is "twenty-one million, two hundred eighteen thousand, seventy-seven".