21509771 has 2 divisors, whose sum is σ = 21509772. Its totient is φ = 21509770.

The previous prime is 21509737. The next prime is 21509783. The reversal of 21509771 is 17790512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21509771 - 2¹⁴ = 21493387 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21509701) 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, 10754885 + 10754886.

It is an arithmetic number, because the mean of its divisors is an integer number (10754886).

Almost surely, 2^21509771 is an apocalyptic number.

21509771 is a deficient number, since it is larger than the sum of its proper divisors (1).

21509771 is an equidigital number, since it uses as much as digits as its factorization.

21509771 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4410, while the sum is 32.

The square root of 21509771 is about 4637.8627620920. The cubic root of 21509771 is about 278.1070055437.

The spelling of 21509771 in words is "twenty-one million, five hundred nine thousand, seven hundred seventy-one".