7821565 has 4 divisors (see below), whose sum is σ = 9385884. Its totient is φ = 6257248.

The previous prime is 7821563. The next prime is 7821589. The reversal of 7821565 is 5651287.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5651287 = 521 ⋅10847.

It can be written as a sum of positive squares in 2 ways, for example, as 2490084 + 5331481 = 1578^2 + 2309^2 .

It is a cyclic number.

It is not a de Polignac number, because 7821565 - 2¹ = 7821563 is a prime.

It is a super-2 number, since 2×7821565² = 122353758098450, which contains 22 as substring.

It is a Duffinian number.

7821565 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 7821565.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7821563) 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, 782152 + ... + 782161.

It is an arithmetic number, because the mean of its divisors is an integer number (2346471).

Almost surely, 2^7821565 is an apocalyptic number.

It is an amenable number.

7821565 is a deficient number, since it is larger than the sum of its proper divisors (1564319).

7821565 is a wasteful number, since it uses less digits than its factorization.

7821565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1564318.

The product of its digits is 16800, while the sum is 34.

The square root of 7821565 is about 2796.7060982520. The cubic root of 7821565 is about 198.5018473815.

It can be divided in two parts, 782 and 1565, that multiplied together give a triangular number (1223830 = T₁₅₆₄).

The spelling of 7821565 in words is "seven million, eight hundred twenty-one thousand, five hundred sixty-five".