1961671956409 has 27 divisors (see below), whose sum is σ = 2172718341423. Its totient is φ = 1769794369200.

The previous prime is 1961671956401. The next prime is 1961671956479. The reversal of 1961671956409 is 9046591761691.

The square root of 1961671956409 is 1400597.

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

It can be written as a sum of positive squares in only one way, i.e., 574996141225 + 1386675815184 = 758285^2 + 1177572^2 .

It is not a de Polignac number, because 1961671956409 - 2³ = 1961671956401 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1961671956401) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 2418830614 + ... + 2418831424.

Almost surely, 2^{1961671956409} is an apocalyptic number.

1961671956409 is the 1400597-th square number.

1961671956409 is the 700299-th centered octagonal number.

It is an amenable number.

1961671956409 is a deficient number, since it is larger than the sum of its proper divisors (211046385014).

1961671956409 is an frugal number, since it uses more digits than its factorization.

1961671956409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1958 (or 979 counting only the distinct ones).

The product of its (nonzero) digits is 22044960, while the sum is 64.

Multiplying 1961671956409 by its sum of digits (64), we get a square (125547005210176 = 11204776²).

The spelling of 1961671956409 in words is "one trillion, nine hundred sixty-one billion, six hundred seventy-one million, nine hundred fifty-six thousand, four hundred nine".