661638784 has 16 divisors (see below), whose sum is σ = 1318108770. Its totient is φ = 330819328.

The previous prime is 661638781. The next prime is 661638839. The reversal of 661638784 is 487836166.

It can be written as a sum of positive squares in only one way, i.e., 489294400 + 172344384 = 22120^2 + 13128^2 .

It is a tau number, because it is divible by the number of its divisors (16).

It is not an unprimeable number, because it can be changed into a prime (661638781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2584399 + ... + 2584654.

Almost surely, 2^661638784 is an apocalyptic number.

661638784 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

661638784 is a deficient number, since it is larger than the sum of its proper divisors (656469986).

661638784 is an equidigital number, since it uses as much as digits as its factorization.

661638784 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5169067 (or 5169055 counting only the distinct ones).

The product of its digits is 1161216, while the sum is 49.

The square root of 661638784 is about 25722.3401734757. The cubic root of 661638784 is about 871.3787905068.

It can be divided in two parts, 66163 and 8784, that added together give a palindrome (74947).

The spelling of 661638784 in words is "six hundred sixty-one million, six hundred thirty-eight thousand, seven hundred eighty-four".