1921681 has 2 divisors, whose sum is σ = 1921682. Its totient is φ = 1921680.

The previous prime is 1921657. The next prime is 1921687. The reversal of 1921681 is 1861291.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1345600 + 576081 = 1160^2 + 759^2 .

It is a cyclic number.

It is not a de Polignac number, because 1921681 - 2⁷ = 1921553 is a prime.

It is a super-2 number, since 2×1921681² = 7385715731522, which contains 22 as substring.

It is an Ulam number.

It is a plaindrome in base 7.

It is not a weakly prime, because it can be changed into another prime (1921687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 960840 + 960841.

It is an arithmetic number, because the mean of its divisors is an integer number (960841).

2^1921681 is an apocalyptic number.

It is an amenable number.

1921681 is a deficient number, since it is larger than the sum of its proper divisors (1).

1921681 is an equidigital number, since it uses as much as digits as its factorization.

1921681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 864, while the sum is 28.

The square root of 1921681 is about 1386.2470919717. The cubic root of 1921681 is about 124.3255622814.

The spelling of 1921681 in words is "one million, nine hundred twenty-one thousand, six hundred eighty-one".