651821 has 2 divisors, whose sum is σ = 651822. Its totient is φ = 651820.

The previous prime is 651811. The next prime is 651839. The reversal of 651821 is 128156.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 570025 + 81796 = 755^2 + 286^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-651821 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (651811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 325910 + 325911.

It is an arithmetic number, because the mean of its divisors is an integer number (325911).

2⁶⁵¹⁸²¹ is an apocalyptic number.

It is an amenable number.

651821 is a deficient number, since it is larger than the sum of its proper divisors (1).

651821 is an equidigital number, since it uses as much as digits as its factorization.

651821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 480, while the sum is 23.

The square root of 651821 is about 807.3543212246. The cubic root of 651821 is about 86.7047285151.

Adding to 651821 its reverse (128156), we get a palindrome (779977).

The spelling of 651821 in words is "six hundred fifty-one thousand, eight hundred twenty-one".