1721651021689 has 9 divisors (see below), whose sum is σ = 1738664845893. Its totient is φ = 1704802127292.

The previous prime is 1721651021659. The next prime is 1721651021731. The reversal of 1721651021689 is 9861201561271.

The square root of 1721651021689 is 1312117.

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

It is not a de Polignac number, because 1721651021689 - 2²¹ = 1721648924537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1721651021659) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 135141682 + ... + 135154420.

It is an arithmetic number, because the mean of its divisors is an integer number (193184982877).

Almost surely, 2^{1721651021689} is an apocalyptic number.

1721651021689 is the 1312117-th square number.

1721651021689 is the 656059-th centered octagonal number.

It is an amenable number.

1721651021689 is a deficient number, since it is larger than the sum of its proper divisors (17013824204).

1721651021689 is an frugal number, since it uses more digits than its factorization.

1721651021689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25684 (or 12842 counting only the distinct ones).

The product of its (nonzero) digits is 362880, while the sum is 49.

Multiplying 1721651021689 by its sum of digits (49), we get a square (84360900062761 = 9184819²).

The spelling of 1721651021689 in words is "one trillion, seven hundred twenty-one billion, six hundred fifty-one million, twenty-one thousand, six hundred eighty-nine".