1621639 has 2 divisors, whose sum is σ = 1621640. Its totient is φ = 1621638.

The previous prime is 1621637. The next prime is 1621643. The reversal of 1621639 is 9361261.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1621639 - 2¹ = 1621637 is a prime.

It is a super-3 number, since 3×1621639³ = 12793335704168820357, which contains 333 as substring.

Together with 1621637, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1621637) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810819 + 810820.

It is an arithmetic number, because the mean of its divisors is an integer number (810820).

2^1621639 is an apocalyptic number.

1621639 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621639 is an equidigital number, since it uses as much as digits as its factorization.

1621639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1944, while the sum is 28.

The square root of 1621639 is about 1273.4359033732. The cubic root of 1621639 is about 117.4856237127.

The spelling of 1621639 in words is "one million, six hundred twenty-one thousand, six hundred thirty-nine".