21788281 has 4 divisors (see below), whose sum is σ = 21810064. Its totient is φ = 21766500.

The previous prime is 21788233. The next prime is 21788293. The reversal of 21788281 is 18288712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21788281 - 2¹⁹ = 21263993 is a prime.

It is a super-2 number, since 2×21788281² = 949458377869922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21788281.

It is not an unprimeable number, because it can be changed into a prime (21788201) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9315 + ... + 11416.

It is an arithmetic number, because the mean of its divisors is an integer number (5452516).

Almost surely, 2^21788281 is an apocalyptic number.

21788281 is the 2088-th centered decagonal number.

It is an amenable number.

21788281 is a deficient number, since it is larger than the sum of its proper divisors (21783).

21788281 is a wasteful number, since it uses less digits than its factorization.

21788281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21782.

The product of its digits is 14336, while the sum is 37.

The square root of 21788281 is about 4667.7918762516. The cubic root of 21788281 is about 279.3021781348.

The spelling of 21788281 in words is "twenty-one million, seven hundred eighty-eight thousand, two hundred eighty-one".