66891087521 has 2 divisors, whose sum is σ = 66891087522. Its totient is φ = 66891087520.

The previous prime is 66891087463. The next prime is 66891087587. The reversal of 66891087521 is 12578019866.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 51481341025 + 15409746496 = 226895^2 + 124136^2 .

It is a cyclic number.

It is not a de Polignac number, because 66891087521 - 2⁶ = 66891087457 is a prime.

It is not a weakly prime, because it can be changed into another prime (66891087121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33445543760 + 33445543761.

It is an arithmetic number, because the mean of its divisors is an integer number (33445543761).

Almost surely, 2^66891087521 is an apocalyptic number.

It is an amenable number.

66891087521 is a deficient number, since it is larger than the sum of its proper divisors (1).

66891087521 is an equidigital number, since it uses as much as digits as its factorization.

66891087521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1451520, while the sum is 53.

The spelling of 66891087521 in words is "sixty-six billion, eight hundred ninety-one million, eighty-seven thousand, five hundred twenty-one".