1561781 has 8 divisors (see below), whose sum is σ = 1770720. Its totient is φ = 1365552.

The previous prime is 1561759. The next prime is 1561801. The reversal of 1561781 is 1871651.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1561781 - 2¹⁸ = 1299637 is a prime.

It is a super-2 number, since 2×1561781² = 4878319783922, which contains 22 as substring.

It is a Duffinian number.

It is a nialpdrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1561711) 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 in 7 ways as a sum of consecutive naturals, for example, 2915 + ... + 3408.

It is an arithmetic number, because the mean of its divisors is an integer number (221340).

2^1561781 is an apocalyptic number.

It is an amenable number.

1561781 is a deficient number, since it is larger than the sum of its proper divisors (208939).

1561781 is a wasteful number, since it uses less digits than its factorization.

1561781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6355.

The product of its digits is 1680, while the sum is 29.

The square root of 1561781 is about 1249.7123669069. The cubic root of 1561781 is about 116.0219191635.

It can be divided in two parts, 1561 and 781, that multiplied together give a triangular number (1219141 = T₁₅₆₁).

The spelling of 1561781 in words is "one million, five hundred sixty-one thousand, seven hundred eighty-one".