21505155 has 32 divisors (see below), whose sum is σ = 39705600. Its totient is φ = 9735552.

The previous prime is 21505151. The next prime is 21505157. The reversal of 21505155 is 55150512.

It is not a de Polignac number, because 21505155 - 2² = 21505151 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21505151) 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, 10506 + ... + 12384.

It is an arithmetic number, because the mean of its divisors is an integer number (1240800).

Almost surely, 2^21505155 is an apocalyptic number.

21505155 is a deficient number, since it is larger than the sum of its proper divisors (18200445).

21505155 is a wasteful number, since it uses less digits than its factorization.

21505155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2003.

The product of its (nonzero) digits is 1250, while the sum is 24.

The square root of 21505155 is about 4637.3650923774. The cubic root of 21505155 is about 278.0871101858.

Adding to 21505155 its reverse (55150512), we get a palindrome (76655667).

The spelling of 21505155 in words is "twenty-one million, five hundred five thousand, one hundred fifty-five".