21585757 has 2 divisors, whose sum is σ = 21585758. Its totient is φ = 21585756.

The previous prime is 21585743. The next prime is 21585761. The reversal of 21585757 is 75758512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21585316 + 441 = 4646^2 + 21^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21585757 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21585797) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10792878 + 10792879.

It is an arithmetic number, because the mean of its divisors is an integer number (10792879).

Almost surely, 2^21585757 is an apocalyptic number.

It is an amenable number.

21585757 is a deficient number, since it is larger than the sum of its proper divisors (1).

21585757 is an equidigital number, since it uses as much as digits as its factorization.

21585757 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 98000, while the sum is 40.

The square root of 21585757 is about 4646.0474599384. The cubic root of 21585757 is about 278.4341034556.

The spelling of 21585757 in words is "twenty-one million, five hundred eighty-five thousand, seven hundred fifty-seven".