251221551240 has 128 divisors (see below), whose sum is σ = 822313451520. Its totient is φ = 60892281600.

The previous prime is 251221551239. The next prime is 251221551241. The reversal of 251221551240 is 42155122152.

It is an interprime number because it is at equal distance from previous prime (251221551239) and next prime (251221551241).

It is a super-2 number, since 2×251221551240² (a number of 24 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 251221551198 and 251221551207.

It is not an unprimeable number, because it can be changed into a prime (251221551241) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 11138775 + ... + 11161305.

It is an arithmetic number, because the mean of its divisors is an integer number (6424323840).

Almost surely, 2^251221551240 is an apocalyptic number.

251221551240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

251221551240 is an abundant number, since it is smaller than the sum of its proper divisors (571091900280).

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

251221551240 is a wasteful number, since it uses less digits than its factorization.

251221551240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31003 (or 30999 counting only the distinct ones).

The product of its (nonzero) digits is 8000, while the sum is 30.

Adding to 251221551240 its reverse (42155122152), we get a palindrome (293376673392).

The spelling of 251221551240 in words is "two hundred fifty-one billion, two hundred twenty-one million, five hundred fifty-one thousand, two hundred forty".