1981396879640 has 128 divisors (see below), whose sum is σ = 4621563648000. Its totient is φ = 764157888000.

The previous prime is 1981396879639. The next prime is 1981396879667. The reversal of 1981396879640 is 469786931891.

It is a Cunningham number, because it is equal to 1407621²-1.

It is a super-3 number, since 3×1981396879640³ (a number of 38 digits) contains 333 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 28117250 + ... + 28187630.

It is an arithmetic number, because the mean of its divisors is an integer number (36105966000).

Almost surely, 2^{1981396879640} is an apocalyptic number.

1981396879640 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1981396879640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2310781824000).

1981396879640 is an abundant number, since it is smaller than the sum of its proper divisors (2640166768360).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1981396879640 is a wasteful number, since it uses less digits than its factorization.

1981396879640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70681 (or 70677 counting only the distinct ones).

The product of its (nonzero) digits is 141087744, while the sum is 71.

The spelling of 1981396879640 in words is "one trillion, nine hundred eighty-one billion, three hundred ninety-six million, eight hundred seventy-nine thousand, six hundred forty".