2556821 has 2 divisors, whose sum is σ = 2556822. Its totient is φ = 2556820.

The previous prime is 2556803. The next prime is 2556839. The reversal of 2556821 is 1286552.

It is a balanced prime because it is at equal distance from previous prime (2556803) and next prime (2556839).

It can be written as a sum of positive squares in only one way, i.e., 1322500 + 1234321 = 1150^2 + 1111^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2556821 is a prime.

It is equal to p₁₈₆₉₂₃ and since 2556821 and 186923 have the same sum of digits, it is a Honaker prime.

It is a plaindrome in base 15.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2556871) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1278410 + 1278411.

It is an arithmetic number, because the mean of its divisors is an integer number (1278411).

2^2556821 is an apocalyptic number.

It is an amenable number.

2556821 is a deficient number, since it is larger than the sum of its proper divisors (1).

2556821 is an equidigital number, since it uses as much as digits as its factorization.

2556821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4800, while the sum is 29.

The square root of 2556821 is about 1599.0062538965. The cubic root of 2556821 is about 136.7414271380.

The spelling of 2556821 in words is "two million, five hundred fifty-six thousand, eight hundred twenty-one".