691737795666 has 80 divisors (see below), whose sum is σ = 1594888581528. Its totient is φ = 223988544000.

The previous prime is 691737795559. The next prime is 691737795689. The reversal of 691737795666 is 666597737196.

It can be written as a sum of positive squares in 4 ways, for example, as 679353444441 + 12384351225 = 824229^2 + 111285^2 .

It is a junction number, because it is equal to n+sod(n) for n = 691737795594 and 691737795603.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 468346 + ... + 1266026.

Almost surely, 2^691737795666 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 691737795666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (797444290764).

691737795666 is an abundant number, since it is smaller than the sum of its proper divisors (903150785862).

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

691737795666 is a wasteful number, since it uses less digits than its factorization.

691737795666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 797849 (or 797840 counting only the distinct ones).

The product of its digits is 540101520, while the sum is 72.

The spelling of 691737795666 in words is "six hundred ninety-one billion, seven hundred thirty-seven million, seven hundred ninety-five thousand, six hundred sixty-six".