7821661 has 2 divisors, whose sum is σ = 7821662. Its totient is φ = 7821660.

The previous prime is 7821643. The next prime is 7821691. The reversal of 7821661 is 1661287.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 5808100 + 2013561 = 2410^2 + 1419^2 .

It is a cyclic number.

It is not a de Polignac number, because 7821661 - 2⁵ = 7821629 is a prime.

It is a super-2 number, since 2×7821661² = 122356761597842, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (7821601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3910830 + 3910831.

It is an arithmetic number, because the mean of its divisors is an integer number (3910831).

Almost surely, 2^7821661 is an apocalyptic number.

It is an amenable number.

7821661 is a deficient number, since it is larger than the sum of its proper divisors (1).

7821661 is an equidigital number, since it uses as much as digits as its factorization.

7821661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4032, while the sum is 31.

The square root of 7821661 is about 2796.7232612470. The cubic root of 7821661 is about 198.5026594995.

The spelling of 7821661 in words is "seven million, eight hundred twenty-one thousand, six hundred sixty-one".