1681621 has 2 divisors, whose sum is σ = 1681622. Its totient is φ = 1681620.

The previous prime is 1681619. The next prime is 1681639. The reversal of 1681621 is 1261861.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1102500 + 579121 = 1050^2 + 761^2 .

It is an emirp because it is prime and its reverse (1261861) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1681621 - 2¹ = 1681619 is a prime.

Together with 1681619, it forms a pair of twin primes.

1681621 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1681651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 840810 + 840811.

It is an arithmetic number, because the mean of its divisors is an integer number (840811).

2^1681621 is an apocalyptic number.

It is an amenable number.

1681621 is a deficient number, since it is larger than the sum of its proper divisors (1).

1681621 is an equidigital number, since it uses as much as digits as its factorization.

1681621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 576, while the sum is 25.

The square root of 1681621 is about 1296.7733032415. The cubic root of 1681621 is about 118.9166612784.

The spelling of 1681621 in words is "one million, six hundred eighty-one thousand, six hundred twenty-one".