61815821 has 2 divisors, whose sum is σ = 61815822. Its totient is φ = 61815820.

The previous prime is 61815781. The next prime is 61815877. The reversal of 61815821 is 12851816.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 39866596 + 21949225 = 6314^2 + 4685^2 .

It is a cyclic number.

It is not a de Polignac number, because 61815821 - 2¹⁸ = 61553677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (61815121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 30907910 + 30907911.

It is an arithmetic number, because the mean of its divisors is an integer number (30907911).

Almost surely, 2^61815821 is an apocalyptic number.

It is an amenable number.

61815821 is a deficient number, since it is larger than the sum of its proper divisors (1).

61815821 is an equidigital number, since it uses as much as digits as its factorization.

61815821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3840, while the sum is 32.

The square root of 61815821 is about 7862.3037972340. The cubic root of 61815821 is about 395.3968579916.

The spelling of 61815821 in words is "sixty-one million, eight hundred fifteen thousand, eight hundred twenty-one".