6997791971556 has 135 divisors (see below), whose sum is σ = 18394114251513. Its totient is φ = 2319852104640.

The previous prime is 6997791971551. The next prime is 6997791971579. The reversal of 6997791971556 is 6551791977996.

The square root of 6997791971556 is 2645334.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 4729033033956 + 2268758937600 = 2174634^2 + 1506240^2 .

It is a super-2 number, since 2×6997791971556² (a number of 26 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (81).

It is not an unprimeable number, because it can be changed into a prime (6997791971551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 13380099111 + ... + 13380099633.

Almost surely, 2^{6997791971556} is an apocalyptic number.

6997791971556 is the 2645334-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6997791971556

6997791971556 is an abundant number, since it is smaller than the sum of its proper divisors (11396322279957).

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

6997791971556 is an frugal number, since it uses more digits than its factorization.

6997791971556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1624 (or 809 counting only the distinct ones).

The product of its digits is 2025380700, while the sum is 81.

Multiplying 6997791971556 by its sum of digits (81), we get a square (566821149696036 = 23808006²).

6997791971556 divided by its sum of digits (81) gives a square (86392493476 = 293926²).

The spelling of 6997791971556 in words is "six trillion, nine hundred ninety-seven billion, seven hundred ninety-one million, nine hundred seventy-one thousand, five hundred fifty-six".