661551616 has 80 divisors (see below), whose sum is σ = 1457504928. Its totient is φ = 297472000.

The previous prime is 661551589. The next prime is 661551641. The reversal of 661551616 is 616155166.

It is a super-2 number, since 2×661551616² = 875301081264422912, which contains 22 as substring.

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, 568251 + ... + 569413.

Almost surely, 2^661551616 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661551616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (728752464).

661551616 is an abundant number, since it is smaller than the sum of its proper divisors (795953312).

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

661551616 is a wasteful number, since it uses less digits than its factorization.

661551616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1293 (or 1277 counting only the distinct ones).

The product of its digits is 32400, while the sum is 37.

The square root of 661551616 is about 25720.6457150671. The cubic root of 661551616 is about 871.3405220517.

The spelling of 661551616 in words is "six hundred sixty-one million, five hundred fifty-one thousand, six hundred sixteen".