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'43' ('forty-three') is the natural number following 42 and preceding 44.

Cardinal	43 forty-three
Ordinal	43rd forty-third
Factorization	''prime''
Divisors	1, 43
Roman numeral	XLIII
Binary	101011
Hexadecimal	2B

Contents

In mathematics

In science

Astronomy

In sports

In other fields

Historical years

In mathematics

'Forty-three' is the 14th smallest prime number. The previous is forty-one, with which it comprises a twin prime, and the next is forty-seven. 43 is the smallest prime that is not a Chen prime. It is also the third Wagstaff prime.
43 is the fourth term of Sylvester's sequence, one more than the product of the previous terms (2 × 3 × 7).
43 is a centered heptagonal number.
Let a(0) = a(1) = 1, and thenceforth a(n) = (a(0)² + a(1)² + ... + a(n-1)²) / (n-1). This sequence continues 1 1 2 3 5 10 28 154... . Amazingly, a(43) is the first term of this sequence that is not an integer.
43 is a Heegner number.
43 is a repdigit in base 6 (111).
43 is the largest natural number that is not an (original) McNugget number.
This is the smallest number, which draws up as sum of 2,3,4,5 different primes: 43=41+2 43=11+13+19 43=2+11+13+17 43=3+5+7+11+17. The following date magic square illustrates the magic constant as the sum of four primes:

4	15	''17''	07
5	19	''13''	6
20	9	''2''	12
14	0	''11''	18

In science

★ The chemical element with the atomic number 43 is technetium. It has the lowest atomic number of any element that does not possess stable isotopes.

Astronomy

★ Messier object M43, a magnitude 7.0 H II region in the constellation of Orion, a part of the Orion Nebula, and also sometimes known as ''de Mairan's Nebula''

★ The New General Catalogue object NGC 43, a barred spiral galaxy in the constellation Andromeda

★ The Saros number of the solar eclipse series which began on April 29, 1513 BC and ended on June 5, 233 BC . The duration of Saros series 43 was 1280.1 years, and it contained 72 solar eclipses.

★ The Saros number of the lunar eclipse series which began on August 27, 1482 BC and ended on March 15, 70. The duration of Saros series 43 was 1550.5 years, and it contained 87 lunar eclipses.

In sports

In professional sports in the United States, the jersey number 43 has been retired for Jim Norton of Tennessee (NFL) and Dennis Eckersley of the Oakland Athletics.

★ The number for Richard Petty's NASCAR race car when he won his 7 Winston Cup Championships. He also won 200 races in his career, 95% of them in the famous #43.

★ The number worn by Derby County Goalkeeper Stephen Bywater in memory of his ex-goalkeeping coach Les Sealey who died at the age of 43 in 2001.
Mad Magazine created the game 43-Man Squamish.

In other fields

'Forty-three' is:

★ The designation of Interstate 43, a freeway in Wisconsin.

★ The code for direct dial international phone calls to Austria.

Historical years

'43 A.D.', 43 B.C., 1943, 2043, etc.