1621621 has 2 divisors, whose sum is σ = 1621622. Its totient is φ = 1621620.

The previous prime is 1621619. The next prime is 1621637. The reversal of 1621621 is 1261261.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1179396 + 442225 = 1086^2 + 665^2 .

It is an emirp because it is prime and its reverse (1261261) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1621621 - 2¹ = 1621619 is a prime.

Together with 1621619, it forms a pair of twin primes.

It is a Chen prime.

1621621 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1621421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810810 + 810811.

It is an arithmetic number, because the mean of its divisors is an integer number (810811).

2^1621621 is an apocalyptic number.

It is an amenable number.

1621621 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621621 is an equidigital number, since it uses as much as digits as its factorization.

1621621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 144, while the sum is 19.

The square root of 1621621 is about 1273.4288358601. The cubic root of 1621621 is about 117.4851890189.

Adding to 1621621 its reverse (1261261), we get a palindrome (2882882).

The spelling of 1621621 in words is "one million, six hundred twenty-one thousand, six hundred twenty-one".