21515443657 has 2 divisors, whose sum is σ = 21515443658. Its totient is φ = 21515443656.

The previous prime is 21515443643. The next prime is 21515443667. The reversal of 21515443657 is 75634451512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12180212496 + 9335231161 = 110364^2 + 96619^2 .

It is a cyclic number.

It is not a de Polignac number, because 21515443657 - 2¹⁹ = 21514919369 is a prime.

It is not a weakly prime, because it can be changed into another prime (21515443637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10757721828 + 10757721829.

It is an arithmetic number, because the mean of its divisors is an integer number (10757721829).

Almost surely, 2^21515443657 is an apocalyptic number.

It is an amenable number.

21515443657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21515443657 is an equidigital number, since it uses as much as digits as its factorization.

21515443657 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 504000, while the sum is 43.

The spelling of 21515443657 in words is "twenty-one billion, five hundred fifteen million, four hundred forty-three thousand, six hundred fifty-seven".