661155551 has 8 divisors (see below), whose sum is σ = 800053920. Its totient is φ = 533369088.

The previous prime is 661155541. The next prime is 661155563. The reversal of 661155551 is 155551166.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 661155551 - 2¹⁸ = 660893407 is a prime.

It is a super-2 number, since 2×661155551² = 874253325236227202, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661155541) 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 in 7 ways as a sum of consecutive naturals, for example, 2777846 + ... + 2778083.

It is an arithmetic number, because the mean of its divisors is an integer number (100006740).

Almost surely, 2^661155551 is an apocalyptic number.

661155551 is a deficient number, since it is larger than the sum of its proper divisors (138898369).

661155551 is a wasteful number, since it uses less digits than its factorization.

661155551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5555953.

The product of its digits is 22500, while the sum is 35.

The square root of 661155551 is about 25712.9452027573. The cubic root of 661155551 is about 871.1665994283.

The spelling of 661155551 in words is "six hundred sixty-one million, one hundred fifty-five thousand, five hundred fifty-one".