66561155537 has 4 divisors (see below), whose sum is σ = 66773811300. Its totient is φ = 66348499776.

The previous prime is 66561155503. The next prime is 66561155543. The reversal of 66561155537 is 73555116566.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2086296976 + 64474858561 = 45676^2 + 253919^2 .

It is a cyclic number.

It is not a de Polignac number, because 66561155537 - 2¹² = 66561151441 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66561155237) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106327412 + ... + 106328037.

It is an arithmetic number, because the mean of its divisors is an integer number (16693452825).

Almost surely, 2^66561155537 is an apocalyptic number.

It is an amenable number.

66561155537 is a deficient number, since it is larger than the sum of its proper divisors (212655763).

66561155537 is a wasteful number, since it uses less digits than its factorization.

66561155537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 212655762.

The product of its digits is 2835000, while the sum is 50.

The spelling of 66561155537 in words is "sixty-six billion, five hundred sixty-one million, one hundred fifty-five thousand, five hundred thirty-seven".