21505253 has 16 divisors (see below), whose sum is σ = 27979776. Its totient is φ = 16027440.

The previous prime is 21505243. The next prime is 21505259. The reversal of 21505253 is 35250512.

It is not a de Polignac number, because 21505253 - 2²² = 17310949 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505259) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4301 + ... + 7842.

It is an arithmetic number, because the mean of its divisors is an integer number (1748736).

Almost surely, 2^21505253 is an apocalyptic number.

21505253 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

It is an amenable number.

21505253 is a deficient number, since it is larger than the sum of its proper divisors (6474523).

21505253 is a wasteful number, since it uses less digits than its factorization.

21505253 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12184.

The product of its (nonzero) digits is 1500, while the sum is 23.

The square root of 21505253 is about 4637.3756587104. The cubic root of 21505253 is about 278.0875326038.

Adding to 21505253 its reverse (35250512), we get a palindrome (56755765).

The spelling of 21505253 in words is "twenty-one million, five hundred five thousand, two hundred fifty-three".