51721861 has 2 divisors, whose sum is σ = 51721862. Its totient is φ = 51721860.

The previous prime is 51721847. The next prime is 51721897. The reversal of 51721861 is 16812715.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 32273761 + 19448100 = 5681^2 + 4410^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-51721861 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51721801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25860930 + 25860931.

It is an arithmetic number, because the mean of its divisors is an integer number (25860931).

Almost surely, 2^51721861 is an apocalyptic number.

It is an amenable number.

51721861 is a deficient number, since it is larger than the sum of its proper divisors (1).

51721861 is an equidigital number, since it uses as much as digits as its factorization.

51721861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3360, while the sum is 31.

The square root of 51721861 is about 7191.7912233323. The cubic root of 51721861 is about 372.5844404160.

The spelling of 51721861 in words is "fifty-one million, seven hundred twenty-one thousand, eight hundred sixty-one".