21305505 has 32 divisors (see below), whose sum is σ = 38876544. Its totient is φ = 9870336.

The previous prime is 21305497. The next prime is 21305507. The reversal of 21305505 is 50550312.

It is not a de Polignac number, because 21305505 - 2³ = 21305497 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21305507) 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, 102 + ... + 6528.

It is an arithmetic number, because the mean of its divisors is an integer number (1214892).

Almost surely, 2^21305505 is an apocalyptic number.

It is an amenable number.

21305505 is a deficient number, since it is larger than the sum of its proper divisors (17571039).

21305505 is a wasteful number, since it uses less digits than its factorization.

21305505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6465.

The product of its (nonzero) digits is 750, while the sum is 21.

The square root of 21305505 is about 4615.7886650062. The cubic root of 21305505 is about 277.2238629615.

Adding to 21305505 its reverse (50550312), we get a palindrome (71855817).

The spelling of 21305505 in words is "twenty-one million, three hundred five thousand, five hundred five".