21681769 has 2 divisors, whose sum is σ = 21681770. Its totient is φ = 21681768.

The previous prime is 21681739. The next prime is 21681797. The reversal of 21681769 is 96718612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21049744 + 632025 = 4588^2 + 795^2 .

It is a cyclic number.

It is not a de Polignac number, because 21681769 - 2¹³ = 21673577 is a prime.

It is a super-2 number, since 2×21681769² = 940198213938722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21681739) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10840884 + 10840885.

It is an arithmetic number, because the mean of its divisors is an integer number (10840885).

Almost surely, 2^21681769 is an apocalyptic number.

It is an amenable number.

21681769 is a deficient number, since it is larger than the sum of its proper divisors (1).

21681769 is an equidigital number, since it uses as much as digits as its factorization.

21681769 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 36288, while the sum is 40.

The square root of 21681769 is about 4656.3686494950. The cubic root of 21681769 is about 278.8463116421.

The spelling of 21681769 in words is "twenty-one million, six hundred eighty-one thousand, seven hundred sixty-nine".