638995690 has 16 divisors (see below), whose sum is σ = 1161582120. Its totient is φ = 253067200.

The previous prime is 638995681. The next prime is 638995699. The reversal of 638995690 is 96599836.

It is an interprime number because it is at equal distance from previous prime (638995681) and next prime (638995699).

It can be written as a sum of positive squares in 4 ways, for example, as 533748609 + 105247081 = 23103^2 + 10259^2 .

It is a super-2 number, since 2×638995690² = 816630983677152200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (638995699) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 315325 + ... + 317344.

Almost surely, 2^638995690 is an apocalyptic number.

638995690 is a deficient number, since it is larger than the sum of its proper divisors (522586430).

638995690 is a wasteful number, since it uses less digits than its factorization.

638995690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 632777.

The product of its (nonzero) digits is 3149280, while the sum is 55.

The square root of 638995690 is about 25278.3640689029. The cubic root of 638995690 is about 861.3228649532.

The spelling of 638995690 in words is "six hundred thirty-eight million, nine hundred ninety-five thousand, six hundred ninety".