21279757 has 2 divisors, whose sum is σ = 21279758. Its totient is φ = 21279756.

The previous prime is 21279749. The next prime is 21279781. The reversal of 21279757 is 75797212.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20331081 + 948676 = 4509^2 + 974^2 .

It is a cyclic number.

It is not a de Polignac number, because 21279757 - 2³ = 21279749 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21279737) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10639878 + 10639879.

It is an arithmetic number, because the mean of its divisors is an integer number (10639879).

Almost surely, 2^21279757 is an apocalyptic number.

It is an amenable number.

21279757 is a deficient number, since it is larger than the sum of its proper divisors (1).

21279757 is an equidigital number, since it uses as much as digits as its factorization.

21279757 is an evil number, because the sum of its binary digits is even.

The product of its digits is 61740, while the sum is 40.

The square root of 21279757 is about 4612.9986993278. The cubic root of 21279757 is about 277.1121416420.

The spelling of 21279757 in words is "twenty-one million, two hundred seventy-nine thousand, seven hundred fifty-seven".