661155555491 has 4 divisors (see below), whose sum is σ = 689901449232. Its totient is φ = 632409661752.

The previous prime is 661155555469. The next prime is 661155555517. The reversal of 661155555491 is 194555551166.

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

It is a cyclic number.

It is not a de Polignac number, because 661155555491 - 2⁶ = 661155555427 is a prime.

It is a super-2 number, since 2×661155555491² (a number of 24 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (661155555691) 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, 14372946836 + ... + 14372946881.

It is an arithmetic number, because the mean of its divisors is an integer number (172475362308).

Almost surely, 2^661155555491 is an apocalyptic number.

661155555491 is a deficient number, since it is larger than the sum of its proper divisors (28745893741).

661155555491 is a wasteful number, since it uses less digits than its factorization.

661155555491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28745893740.

The product of its digits is 4050000, while the sum is 53.

The spelling of 661155555491 in words is "six hundred sixty-one billion, one hundred fifty-five million, five hundred fifty-five thousand, four hundred ninety-one".