661563811 has 8 divisors (see below), whose sum is σ = 685461024. Its totient is φ = 637983360.

The previous prime is 661563803. The next prime is 661563827. The reversal of 661563811 is 118365166.

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

It is a cyclic number.

It is not a de Polignac number, because 661563811 - 2³ = 661563803 is a prime.

It is a super-3 number, since 3×661563811³ (a number of 27 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661563841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 74935 + ... + 83296.

It is an arithmetic number, because the mean of its divisors is an integer number (85682628).

Almost surely, 2^661563811 is an apocalyptic number.

661563811 is a deficient number, since it is larger than the sum of its proper divisors (23897213).

661563811 is a wasteful number, since it uses less digits than its factorization.

661563811 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 158381.

The product of its digits is 25920, while the sum is 37.

The square root of 661563811 is about 25720.8827803402. The cubic root of 661563811 is about 871.3458760972.

The spelling of 661563811 in words is "six hundred sixty-one million, five hundred sixty-three thousand, eight hundred eleven".