661838640 has 40 divisors (see below), whose sum is σ = 2051700528. Its totient is φ = 176490240.

The previous prime is 661838633. The next prime is 661838651. The reversal of 661838640 is 46838166.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (40).

It is a junction number, because it is equal to n+sod(n) for n = 661838592 and 661838601.

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, 1378591 + ... + 1379070.

Almost surely, 2^661838640 is an apocalyptic number.

661838640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

661838640 is an abundant number, since it is smaller than the sum of its proper divisors (1389861888).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661838640 is a wasteful number, since it uses less digits than its factorization.

661838640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2757677 (or 2757671 counting only the distinct ones).

The product of its (nonzero) digits is 165888, while the sum is 42.

The square root of 661838640 is about 25726.2247521862. The cubic root of 661838640 is about 871.4665185098.

The spelling of 661838640 in words is "six hundred sixty-one million, eight hundred thirty-eight thousand, six hundred forty".