16631561 has 6 divisors (see below), whose sum is σ = 16995210. Its totient is φ = 16275536.

The previous prime is 16631557. The next prime is 16631567. The reversal of 16631561 is 16513661.

It can be written as a sum of positive squares in only one way, i.e., 13097161 + 3534400 = 3619^2 + 1880^2 .

It is not a de Polignac number, because 16631561 - 2² = 16631557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16631567) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1556 + ... + 5973.

It is an arithmetic number, because the mean of its divisors is an integer number (2832535).

Almost surely, 2^16631561 is an apocalyptic number.

It is an amenable number.

16631561 is a deficient number, since it is larger than the sum of its proper divisors (363649).

16631561 is an frugal number, since it uses more digits than its factorization.

16631561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7623 (or 7576 counting only the distinct ones).

The product of its digits is 3240, while the sum is 29.

The square root of 16631561 is about 4078.1810896526. The cubic root of 16631561 is about 255.2570060395.

The spelling of 16631561 in words is "sixteen million, six hundred thirty-one thousand, five hundred sixty-one".