1687648561 has 3 divisors (see below), whose sum is σ = 1687689643.
Its totient is φ = 1687607480.
The previous prime is 1687648553. The next prime is 1687648579. The reversal of 1687648561 is 1658467861.
The square root of 1687648561 is 41081.
It is a perfect power (a square), and thus also a powerful number.
It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1658467861 = 17 ⋅97556933.
It can be written as a sum of positive squares in only one way, i.e., 709210161 + 978438400 = 26631^2 + 31280^2
It is not a de Polignac number, because 1687648561 - 23 = 1687648553 is a prime.
It is a Duffinian number.
It is a junction number, because it is equal to n+sod(n) for n = 1687648499 and 1687648508.
It is not an unprimeable number, because it can be changed into a prime (1687648541) by changing a digit.
It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 20541 + ... + 61621.
Almost surely, 21687648561 is an apocalyptic number.
1687648561 is the 41081-st square number.
1687648561 is the 20541-st centered octagonal number.
It is an amenable number.
1687648561 is a deficient number, since it is larger than the sum of its proper divisors (41082).
1687648561 is an frugal number, since it uses more digits than its factorization.
1687648561 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 82162 (or 41081 counting only the distinct ones).
The product of its digits is 1935360, while the sum is 52.
The cubic root of 1687648561 is about 1190.5857251195.
The spelling of 1687648561 in words is "one billion, six hundred eighty-seven million, six hundred forty-eight thousand, five hundred sixty-one".