1561639 has 2 divisors, whose sum is σ = 1561640. Its totient is φ = 1561638.

The previous prime is 1561633. The next prime is 1561657. The reversal of 1561639 is 9361651.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1561639 - 2⁵ = 1561607 is a prime.

It is a Chen prime.

It is equal to p₁₁₈₄₈₉ and since 1561639 and 118489 have the same sum of digits, it is a Honaker prime.

It is a zygodrome in base 3.

It is a self number, because there is not a number n which added to its sum of digits gives 1561639.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1561633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780819 + 780820.

It is an arithmetic number, because the mean of its divisors is an integer number (780820).

2^1561639 is an apocalyptic number.

1561639 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561639 is an equidigital number, since it uses as much as digits as its factorization.

1561639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4860, while the sum is 31.

The square root of 1561639 is about 1249.6555525424. The cubic root of 1561639 is about 116.0184027482.

The spelling of 1561639 in words is "one million, five hundred sixty-one thousand, six hundred thirty-nine".