21641509 has 2 divisors, whose sum is σ = 21641510. Its totient is φ = 21641508.

The previous prime is 21641483. The next prime is 21641537. The reversal of 21641509 is 90514612.

It is an a-pointer prime, because the next prime (21641537) can be obtained adding 21641509 to its sum of digits (28).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14062500 + 7579009 = 3750^2 + 2753^2 .

It is a cyclic number.

It is not a de Polignac number, because 21641509 - 2⁷ = 21641381 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21641579) 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, 10820754 + 10820755.

It is an arithmetic number, because the mean of its divisors is an integer number (10820755).

Almost surely, 2^21641509 is an apocalyptic number.

It is an amenable number.

21641509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21641509 is an equidigital number, since it uses as much as digits as its factorization.

21641509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21641509 is about 4652.0435294610. The cubic root of 21641509 is about 278.6736118919.

The spelling of 21641509 in words is "twenty-one million, six hundred forty-one thousand, five hundred nine".