21218461 has 4 divisors (see below), whose sum is σ = 23147424. Its totient is φ = 19289500.

The previous prime is 21218441. The next prime is 21218467. The reversal of 21218461 is 16481212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21218461 - 2⁵ = 21218429 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 (21218467) 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, 964465 + ... + 964486.

It is an arithmetic number, because the mean of its divisors is an integer number (5786856).

Almost surely, 2^21218461 is an apocalyptic number.

It is an amenable number.

21218461 is a deficient number, since it is larger than the sum of its proper divisors (1928963).

21218461 is a wasteful number, since it uses less digits than its factorization.

21218461 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1928962.

The product of its digits is 768, while the sum is 25.

The square root of 21218461 is about 4606.3500735398. The cubic root of 21218461 is about 276.8458133947.

Adding to 21218461 its reverse (16481212), we get a palindrome (37699673).

The spelling of 21218461 in words is "twenty-one million, two hundred eighteen thousand, four hundred sixty-one".