1620781 has 4 divisors (see below), whose sum is σ = 1676700. Its totient is φ = 1564864.

The previous prime is 1620769. The next prime is 1620803. The reversal of 1620781 is 1870261.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1870261 = 31 ⋅60331.

It can be written as a sum of positive squares in 2 ways, for example, as 1177225 + 443556 = 1085^2 + 666^2 .

It is a cyclic number.

It is not a de Polignac number, because 1620781 - 2¹⁹ = 1096493 is a prime.

It is a super-2 number, since 2×1620781² = 5253862099922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1620881) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27916 + ... + 27973.

It is an arithmetic number, because the mean of its divisors is an integer number (419175).

2^1620781 is an apocalyptic number.

1620781 is the 681-st centered heptagonal number.

It is an amenable number.

1620781 is a deficient number, since it is larger than the sum of its proper divisors (55919).

1620781 is an equidigital number, since it uses as much as digits as its factorization.

1620781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55918.

The product of its (nonzero) digits is 672, while the sum is 25.

The square root of 1620781 is about 1273.0989749426. The cubic root of 1620781 is about 117.4648997315.

It can be divided in two parts, 1620 and 781, that added together give a 4-th power (2401 = 7⁴).

The spelling of 1620781 in words is "one million, six hundred twenty thousand, seven hundred eighty-one".