1561321988 has 6 divisors (see below), whose sum is σ = 2732313486. Its totient is φ = 780660992.

The previous prime is 1561321969. The next prime is 1561322003. The reversal of 1561321988 is 8891231651.

It can be written as a sum of positive squares in only one way, i.e., 1523965444 + 37356544 = 39038^2 + 6112^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195165245 + ... + 195165252.

It is an arithmetic number, because the mean of its divisors is an integer number (455385581).

Almost surely, 2^1561321988 is an apocalyptic number.

It is an amenable number.

1561321988 is a deficient number, since it is larger than the sum of its proper divisors (1170991498).

1561321988 is a wasteful number, since it uses less digits than its factorization.

1561321988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 390330501 (or 390330499 counting only the distinct ones).

The product of its digits is 103680, while the sum is 44.

The square root of 1561321988 is about 39513.5671383893. The cubic root of 1561321988 is about 1160.1055165610.

The spelling of 1561321988 in words is "one billion, five hundred sixty-one million, three hundred twenty-one thousand, nine hundred eighty-eight".