638974781 has 2 divisors, whose sum is σ = 638974782. Its totient is φ = 638974780.

The previous prime is 638974751. The next prime is 638974813. The reversal of 638974781 is 187479836.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 434055556 + 204919225 = 20834^2 + 14315^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-638974781 is a prime.

It is a super-2 number, since 2×638974781² = 816577541507995922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638974751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319487390 + 319487391.

It is an arithmetic number, because the mean of its divisors is an integer number (319487391).

Almost surely, 2^638974781 is an apocalyptic number.

It is an amenable number.

638974781 is a deficient number, since it is larger than the sum of its proper divisors (1).

638974781 is an equidigital number, since it uses as much as digits as its factorization.

638974781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2032128, while the sum is 53.

The square root of 638974781 is about 25277.9504904967. The cubic root of 638974781 is about 861.3134702126.

The spelling of 638974781 in words is "six hundred thirty-eight million, nine hundred seventy-four thousand, seven hundred eighty-one".