51621781 has 2 divisors, whose sum is σ = 51621782. Its totient is φ = 51621780.

The previous prime is 51621763. The next prime is 51621793. The reversal of 51621781 is 18712615.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 45346756 + 6275025 = 6734^2 + 2505^2 .

It is a cyclic number.

It is not a de Polignac number, because 51621781 - 2¹³ = 51613589 is a prime.

It is a super-2 number, since 2×51621781² = 5329616547223922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51621721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25810890 + 25810891.

It is an arithmetic number, because the mean of its divisors is an integer number (25810891).

Almost surely, 2^51621781 is an apocalyptic number.

It is an amenable number.

51621781 is a deficient number, since it is larger than the sum of its proper divisors (1).

51621781 is an equidigital number, since it uses as much as digits as its factorization.

51621781 is an odious number, because the sum of its binary digits is odd.

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

The square root of 51621781 is about 7184.8299214386. The cubic root of 51621781 is about 372.3439726109.

The spelling of 51621781 in words is "fifty-one million, six hundred twenty-one thousand, seven hundred eighty-one".