66515556521 has 2 divisors, whose sum is σ = 66515556522. Its totient is φ = 66515556520.

The previous prime is 66515556487. The next prime is 66515556589. The reversal of 66515556521 is 12565551566.

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., 46747196521 + 19768360000 = 216211^2 + 140600^2 .

It is a cyclic number.

It is not a de Polignac number, because 66515556521 - 2²⁶ = 66448447657 is a prime.

It is not a weakly prime, because it can be changed into another prime (66512556521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33257778260 + 33257778261.

It is an arithmetic number, because the mean of its divisors is an integer number (33257778261).

Almost surely, 2^66515556521 is an apocalyptic number.

It is an amenable number.

66515556521 is a deficient number, since it is larger than the sum of its proper divisors (1).

66515556521 is an equidigital number, since it uses as much as digits as its factorization.

66515556521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1350000, while the sum is 47.

The spelling of 66515556521 in words is "sixty-six billion, five hundred fifteen million, five hundred fifty-six thousand, five hundred twenty-one".