1681857521 has 2 divisors, whose sum is σ = 1681857522. Its totient is φ = 1681857520.

The previous prime is 1681857509. The next prime is 1681857547. The reversal of 1681857521 is 1257581861.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1026497521 + 655360000 = 32039^2 + 25600^2 .

It is a cyclic number.

It is not a de Polignac number, because 1681857521 - 2²⁶ = 1614748657 is a prime.

It is not a weakly prime, because it can be changed into another prime (1681857421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 840928760 + 840928761.

It is an arithmetic number, because the mean of its divisors is an integer number (840928761).

Almost surely, 2^1681857521 is an apocalyptic number.

It is an amenable number.

1681857521 is a deficient number, since it is larger than the sum of its proper divisors (1).

1681857521 is an equidigital number, since it uses as much as digits as its factorization.

1681857521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 134400, while the sum is 44.

The square root of 1681857521 is about 41010.4562398421. The cubic root of 1681857521 is about 1189.2223625025. Note that the first 3 decimals are identical.

The spelling of 1681857521 in words is "one billion, six hundred eighty-one million, eight hundred fifty-seven thousand, five hundred twenty-one".