51721961 has 4 divisors (see below), whose sum is σ = 52569924. Its totient is φ = 50874000.

The previous prime is 51721927. The next prime is 51721997. The reversal of 51721961 is 16912715.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19855936 + 31866025 = 4456^2 + 5645^2 .

It is not a de Polignac number, because 51721961 - 2⁶ = 51721897 is a prime.

It is a super-2 number, since 2×51721961² = 5350322499371042, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (51721921) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 423890 + ... + 424011.

It is an arithmetic number, because the mean of its divisors is an integer number (13142481).

Almost surely, 2^51721961 is an apocalyptic number.

It is an amenable number.

51721961 is a deficient number, since it is larger than the sum of its proper divisors (847963).

51721961 is an equidigital number, since it uses as much as digits as its factorization.

51721961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 847962.

The product of its digits is 3780, while the sum is 32.

The square root of 51721961 is about 7191.7981756999. The cubic root of 51721961 is about 372.5846805364.

The spelling of 51721961 in words is "fifty-one million, seven hundred twenty-one thousand, nine hundred sixty-one".