21788155 has 12 divisors (see below), whose sum is σ = 27596592. Its totient is φ = 16511760.

The previous prime is 21788149. The next prime is 21788159. The reversal of 21788155 is 55188712.

It is not a de Polignac number, because 21788155 - 2³ = 21788147 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21788159) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4231 + ... + 7840.

It is an arithmetic number, because the mean of its divisors is an integer number (2299716).

Almost surely, 2^21788155 is an apocalyptic number.

21788155 is a deficient number, since it is larger than the sum of its proper divisors (5808437).

21788155 is a wasteful number, since it uses less digits than its factorization.

21788155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12114 (or 12095 counting only the distinct ones).

The product of its digits is 22400, while the sum is 37.

The square root of 21788155 is about 4667.7783794863. The cubic root of 21788155 is about 279.3016397392.

The spelling of 21788155 in words is "twenty-one million, seven hundred eighty-eight thousand, one hundred fifty-five".