638962721 has 2 divisors, whose sum is σ = 638962722. Its totient is φ = 638962720.

The previous prime is 638962717. The next prime is 638962741. The reversal of 638962721 is 127269836.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 569490496 + 69472225 = 23864^2 + 8335^2 .

It is a cyclic number.

It is not a de Polignac number, because 638962721 - 2² = 638962717 is a prime.

It is not a weakly prime, because it can be changed into another prime (638962711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319481360 + 319481361.

It is an arithmetic number, because the mean of its divisors is an integer number (319481361).

Almost surely, 2^638962721 is an apocalyptic number.

It is an amenable number.

638962721 is a deficient number, since it is larger than the sum of its proper divisors (1).

638962721 is an equidigital number, since it uses as much as digits as its factorization.

638962721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 217728, while the sum is 44.

The square root of 638962721 is about 25277.7119415504. The cubic root of 638962721 is about 861.3080513728.

The spelling of 638962721 in words is "six hundred thirty-eight million, nine hundred sixty-two thousand, seven hundred twenty-one".