Properties of the Number 1991

One Thousand Nine Hundred Ninety-One

Basics

Value: 1990 → 1991 → 1992

Parity: odd

Prime: No

Previous Prime: 1987

Next Prime: 1993

Digit Sum: 20

Digital Root: 2

Palindrome: Yes

Factorization: 11 × 181

Divisors: 1, 11, 181, 1991

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 11111000111

Octal: 3707

Duodecimal: 119B

Hexadecimal: 7c7

Square: 3964081

Square Root: 44.62062303464621

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Engel expansion of π. A6784

Number of partitions of n in which no parts are multiples of 3. A726

Number of rucksack partitions of n: every consecutive constant subsequence has a different sum. A353864

Numbers > 1000 such that all the substrings of length = 3 are primes (substrings with leading '0' are considered to be nonprime). A211684

Number T(n,k) of Dyck paths of semilength n having exactly k (possibly overlapping) occurrences of the consecutive step pattern given by the binary expansion of n, where 1=U=(1,1) and 0=D=(1,-1); triangle T(n,k), n>=0, read by rows. A243752

Palindromic in bases 10 and 16. A29731

Moebius transform of A064987, n*σ(n). A69097

Bisection of A001400. A14125

a(n) = n*(3·n² - 1)/2. A4188

Numbers all of whose divisors are palindromic. A62687