661978645 has 8 divisors (see below), whose sum is σ = 794660256. Its totient is φ = 529392336.

The previous prime is 661978637. The next prime is 661978651. The reversal of 661978645 is 546879166.

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 661978645 - 2³ = 661978637 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 661978592 and 661978601.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7527 + ... + 37156.

It is an arithmetic number, because the mean of its divisors is an integer number (99332532).

Almost surely, 2^661978645 is an apocalyptic number.

It is an amenable number.

661978645 is a deficient number, since it is larger than the sum of its proper divisors (132681611).

661978645 is a wasteful number, since it uses less digits than its factorization.

661978645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 47651.

The product of its digits is 2177280, while the sum is 52.

The square root of 661978645 is about 25728.9456643680. The cubic root of 661978645 is about 871.5279640346.

It can be divided in two parts, 6619 and 78645, that added together give a square (85264 = 292²).

The spelling of 661978645 in words is "six hundred sixty-one million, nine hundred seventy-eight thousand, six hundred forty-five".