21007771 has 2 divisors, whose sum is σ = 21007772. Its totient is φ = 21007770.

The previous prime is 21007757. The next prime is 21007781. The reversal of 21007771 is 17770012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21007771 - 2¹⁷ = 20876699 is a prime.

It is not a weakly prime, because it can be changed into another prime (21007741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10503885 + 10503886.

It is an arithmetic number, because the mean of its divisors is an integer number (10503886).

Almost surely, 2^21007771 is an apocalyptic number.

21007771 is a deficient number, since it is larger than the sum of its proper divisors (1).

21007771 is an equidigital number, since it uses as much as digits as its factorization.

21007771 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 686, while the sum is 25.

The square root of 21007771 is about 4583.4235021433. The cubic root of 21007771 is about 275.9264445520.

Adding to 21007771 its reverse (17770012), we get a palindrome (38777783).

The spelling of 21007771 in words is "twenty-one million, seven thousand, seven hundred seventy-one".