1621 has 2 divisors, whose sum is σ = 1622.
Its totient is φ = 1620.
The previous prime is 1619. The next prime is 1627. The reversal of 1621 is 1261.
1621 is nontrivially palindromic in base 13.
It is a weak prime.
It can be written as a sum of positive squares in only one way, i.e., 1521 + 100 = 39^2 + 10^2
It is a cyclic number.
It is not a de Polignac number, because 1621 - 21 = 1619 is a prime.
Together with 1619, it forms a pair of twin primes.
It is a Chen prime.
1621 is an undulating number in base 13.
It is a plaindrome in base 11.
It is a nialpdrome in base 12, base 15 and base 16.
It is a junction number, because it is equal to n+sod(n) for n = 1598 and 1607.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (1627) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810 + 811.
It is an arithmetic number, because the mean of its divisors is an integer number (811).
It is an amenable number.
1621 is a deficient number, since it is larger than the sum of its proper divisors (1).
1621 is an equidigital number, since it uses as much as digits as its factorization.
1621 is an evil number, because the sum of its binary digits is even.
The product of its digits is 12, while the sum is 10.
The square root of 1621 is about 40.2616442784.
The cubic root of 1621 is about 11.7470190114.
Adding to 1621 its reverse (1261), we get a palindrome (2882).
The spelling of 1621 in words is "one thousand, six hundred twenty-one".