644594131621440 has 4480 divisors, whose sum is σ = 3120986656972800. Its totient is φ = 121949975347200.

The previous prime is 644594131621409. The next prime is 644594131621469. The reversal of 644594131621440 is 44126131495446.

644594131621440 is a `hidden beast` number, since 6 + 4 + 4 + 5 + 9 + 4 + 1 + 3 + 1 + 621 + 4 + 4 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is an unprimeable number.

It is a polite number, since it can be written in 639 ways as a sum of consecutive naturals, for example, 676384188004 + ... + 676384188956.

It is an arithmetic number, because the mean of its divisors is an integer number (696648807360).

Almost surely, 2^{644594131621440} is an apocalyptic number.

644594131621440 is a gapful number since it is divisible by the number (60) 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 644594131621440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1560493328486400).

644594131621440 is an abundant number, since it is smaller than the sum of its proper divisors (2476392525351360).

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

644594131621440 is a wasteful number, since it uses less digits than its factorization.

644594131621440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1343 (or 1324 counting only the distinct ones).

The product of its (nonzero) digits is 9953280, while the sum is 54.

The spelling of 644594131621440 in words is "six hundred forty-four trillion, five hundred ninety-four billion, one hundred thirty-one million, six hundred twenty-one thousand, four hundred forty".