21788771 has 2 divisors, whose sum is σ = 21788772. Its totient is φ = 21788770.

The previous prime is 21788749. The next prime is 21788803. The reversal of 21788771 is 17788712.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21788771 is a prime.

It is not a weakly prime, because it can be changed into another prime (21788171) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10894385 + 10894386.

It is an arithmetic number, because the mean of its divisors is an integer number (10894386).

Almost surely, 2^21788771 is an apocalyptic number.

21788771 is a deficient number, since it is larger than the sum of its proper divisors (1).

21788771 is an equidigital number, since it uses as much as digits as its factorization.

21788771 is an evil number, because the sum of its binary digits is even.

The product of its digits is 43904, while the sum is 41.

The square root of 21788771 is about 4667.8443633009. The cubic root of 21788771 is about 279.3042718757.

It can be divided in two parts, 217 and 88771, that added together give a palindrome (88988).

The spelling of 21788771 in words is "twenty-one million, seven hundred eighty-eight thousand, seven hundred seventy-one".