61906913721 has 27 divisors (see below), whose sum is σ = 90091308333. Its totient is φ = 40964243040.

The previous prime is 61906913707. The next prime is 61906913749. The reversal of 61906913721 is 12731960916.

The square root of 61906913721 is 248811.

It is a perfect power (a square), and thus also a powerful number.

61906913721 is a `hidden beast` number, since 6 + 190 + 6 + 91 + 372 + 1 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 335439225 + 61571474496 = 18315^2 + 248136^2 .

It is not a de Polignac number, because 61906913721 - 2⁹ = 61906913209 is a prime.

It is not an unprimeable number, because it can be changed into a prime (61906913021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 147047091 + ... + 147047511.

Almost surely, 2^61906913721 is an apocalyptic number.

61906913721 is the 248811-st square number.

61906913721 is the 124406-th centered octagonal number.

It is an amenable number.

61906913721 is a deficient number, since it is larger than the sum of its proper divisors (28184394612).

61906913721 is an frugal number, since it uses more digits than its factorization.

61906913721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1242 (or 621 counting only the distinct ones).

The product of its (nonzero) digits is 122472, while the sum is 45.

The spelling of 61906913721 in words is "sixty-one billion, nine hundred six million, nine hundred thirteen thousand, seven hundred twenty-one".