131 (one hundred [and] thirty-one) is the natural number following 130 and preceding 132.

131 is a Sophie Germain prime,^[1] an irregular prime,^[2] the second 3-digit palindromic prime, and also a permutable prime with 113 and 311. It can be expressed as the sum of three consecutive primes, 131 = 41 + 43 + 47. 131 is an Eisenstein prime with no imaginary part and real part of the form ${\displaystyle 3n-1}$. Because the next odd number, 133, is a semiprime, 131 is a Chen prime. 131 is an Ulam number.^[3]

131 is a full reptend prime in base 10 (and also in base 2). The decimal expansion of 1/131 repeats the digits 007633587786259541984732824427480916030534351145038167938931 297709923664122137404580152671755725190839694656488549618320 6106870229 indefinitely.

131 is the fifth discriminant of imaginary quadratic fields with class number 5, where the 131st prime number 739 is the fifteenth such discriminant.^[4] Meanwhile, there are conjectured to be a total of 131 discriminants of class number 8 (only one more discriminant could exist).^[5]

• Convair C-131 Samaritan was an American military transport produced from 1954 to 1956
• Strike Fighter Squadron (VFA-131) is a United States Navy F/A-18C Hornet fighter squadron stationed at Naval Air Station Oceana
• Tiger 131 is a German Tiger I heavy tank captured in Tunisia by the British 48th Royal Tank Regiment during World War II
• USNS Mission Santa Barbara (T-AO-131) was a Mission Buenaventura-class fleet oiler during World War II
• USS Bandera (APA-131) was a is a United States Navy Haskell-class attack transport ship during World War II
• USS Buchanan (DD-131) was a United States Navy Wickes-class destroyer
• USS General T. H. Bliss (AP-131) was a United States Navy General G. O. Squier-class transport ship during World War II
• USS Hammann (DE-131) was a United States Navy Edsall-class destroyer escort during World War II
• USS Melucta (AK-131) was a United States Navy Crater-class cargo ship during World War II
• USS Walter X. Young (APD-131) was a ship of the United States Navy during World War II
• ZIL-131 is a 3.5-ton 6x6 army truck

• London Buses route 131 is a Transport for London contracted bus route in London
• The Fiat 131 Mirafiori small/medium family car produced from 1974 to 1984
• STS-131 is a NASA Contingency Logistic Flight (CLF) of the Space Shuttle Atlantis which launched in April 2010

131 is also:

• The year AD 131 or 131 BC
• 131 AH is a year in the Islamic calendar that corresponds to 748 – 749 CE.
• 131 Vala is an inner main belt asteroid
• Iodine-131, or radioiodine, is a radioisotope of iodine for medical and pharmaceutical use
• ACP-131 is the controlling publication for listing of Q codes and Z codes, as published by NATO Allied countries
• Sonnet 131 by William Shakespeare
• 131 is the medical emergency telephone number in Chile
• United States Citizenship and Immigration Services Form I-131 to apply for a travel document, reentry permit, refugee travel document or advance parole
• 131 is the ID3v1 tag equivalent to Indie music

• List of highways numbered 131
• United Nations Security Council Resolution 131