21361605 has 32 divisors (see below), whose sum is σ = 38102400. Its totient is φ = 10156032.

The previous prime is 21361591. The next prime is 21361609. The reversal of 21361605 is 50616312.

It is not a de Polignac number, because 21361605 - 2⁷ = 21361477 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21361609) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2641 + ... + 7049.

It is an arithmetic number, because the mean of its divisors is an integer number (1190700).

Almost surely, 2^21361605 is an apocalyptic number.

It is an amenable number.

21361605 is a deficient number, since it is larger than the sum of its proper divisors (16740795).

21361605 is a wasteful number, since it uses less digits than its factorization.

21361605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4453.

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21361605 is about 4621.8616379117. The cubic root of 21361605 is about 277.4669711522.

Adding to 21361605 its reverse (50616312), we get a palindrome (71977917).

It can be divided in two parts, 2136 and 1605, that added together give a triangular number (3741 = T₈₆).

The spelling of 21361605 in words is "twenty-one million, three hundred sixty-one thousand, six hundred five".