21351605 has 8 divisors (see below), whose sum is σ = 27951264. Its totient is φ = 15528400.

The previous prime is 21351601. The next prime is 21351619. The reversal of 21351605 is 50615312.

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

It is not a de Polignac number, because 21351605 - 2² = 21351601 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21351601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 194051 + ... + 194160.

It is an arithmetic number, because the mean of its divisors is an integer number (3493908).

Almost surely, 2^21351605 is an apocalyptic number.

It is an amenable number.

21351605 is a deficient number, since it is larger than the sum of its proper divisors (6599659).

21351605 is a wasteful number, since it uses less digits than its factorization.

21351605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 388227.

The product of its (nonzero) digits is 900, while the sum is 23.

The square root of 21351605 is about 4620.7796961119. The cubic root of 21351605 is about 277.4236675584.

Adding to 21351605 its reverse (50615312), we get a palindrome (71966917).

The spelling of 21351605 in words is "twenty-one million, three hundred fifty-one thousand, six hundred five".