21518961 has 8 divisors (see below), whose sum is σ = 29939520. Its totient is φ = 13722192.

The previous prime is 21518947. The next prime is 21518969. The reversal of 21518961 is 16981512.

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

It is a de Polignac number, because none of the positive numbers 2^k-21518961 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21518969) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 155866 + ... + 156003.

It is an arithmetic number, because the mean of its divisors is an integer number (3742440).

Almost surely, 2^21518961 is an apocalyptic number.

It is an amenable number.

21518961 is a deficient number, since it is larger than the sum of its proper divisors (8420559).

21518961 is a wasteful number, since it uses less digits than its factorization.

21518961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 311895.

The product of its digits is 4320, while the sum is 33.

The square root of 21518961 is about 4638.8534143687. The cubic root of 21518961 is about 278.1466067631.

The spelling of 21518961 in words is "twenty-one million, five hundred eighteen thousand, nine hundred sixty-one".