1001216781 has 30 divisors (see below), whose sum is σ = 1537330410. Its totient is φ = 649365984.

The previous prime is 1001216771. The next prime is 1001216833. The reversal of 1001216781 is 1876121001.

It can be written as a sum of positive squares in 3 ways, for example, as 882624681 + 118592100 = 29709^2 + 10890^2 .

It is not a de Polignac number, because 1001216781 - 2¹⁰ = 1001215757 is a prime.

It is a super-2 number, since 2×1001216781² = 2004870085112003922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1001216771) by changing a digit.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 106375 + ... + 115403.

It is an arithmetic number, because the mean of its divisors is an integer number (51244347).

Almost surely, 2^1001216781 is an apocalyptic number.

It is an amenable number.

1001216781 is a deficient number, since it is larger than the sum of its proper divisors (536113629).

1001216781 is an frugal number, since it uses more digits than its factorization.

1001216781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9115 (or 9069 counting only the distinct ones).

The product of its (nonzero) digits is 672, while the sum is 27.

The square root of 1001216781 is about 31642.0097496983. The cubic root of 1001216781 is about 1000.4054292716.

Adding to 1001216781 its reverse (1876121001), we get a palindrome (2877337782).

The spelling of 1001216781 in words is "one billion, one million, two hundred sixteen thousand, seven hundred eighty-one".