21218047 has 4 divisors (see below), whose sum is σ = 21360600. Its totient is φ = 21075496.

The previous prime is 21218011. The next prime is 21218059. The reversal of 21218047 is 74081212.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21218047 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 (21218647) 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, 71053 + ... + 71350.

It is an arithmetic number, because the mean of its divisors is an integer number (5340150).

Almost surely, 2^21218047 is an apocalyptic number.

21218047 is a deficient number, since it is larger than the sum of its proper divisors (142553).

21218047 is a wasteful number, since it uses less digits than its factorization.

21218047 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 142552.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21218047 is about 4606.3051353552. The cubic root of 21218047 is about 276.8440128413.

Adding to 21218047 its reverse (74081212), we get a palindrome (95299259).

The spelling of 21218047 in words is "twenty-one million, two hundred eighteen thousand, forty-seven".