Equivalent ... ? Think or start at 35 mm miniature film with the negative/sensor size of 24 x 36 mm = todays Full Frame.
Over the decades the 24 x 36 mm photocamera was sold with a 50 mm optic ( it varies from 40 up till 58 mm). The rangefinder camera, with the fixed standard optic, had a 45 mm optic. Like the Minolta, the first American camera in Space; bought a the drugstore at the end of a street in the U.S.A..
Oscar Barnack, the father of the Leica, prefered a 35 mm optic. He was right, 50 mm is too long for every day pictures.
For portraits anything between 80 and 105 mm will do. Never make portraits with the much too populair 135 mm. Wide angle 28 mm or 24 mm.
So we are finished ? Or do you want more mm ? For birds, sport, nature: 200 mm, 300 mm or 400 mm.
If you got no assistent to carry the load, get yourself two zoom optics, Forget Mister big-mouth-wise-guy, who tells Prime Optics are the best and oversized wide apertures are a must,nonsense !
Mr. Richard Avedon, David Bailey, August Sander etc. had no Bokeh photoos nor wide apertures. Stop down to f/11 or f/64. Use a tripod or 6400 ISO.
Do you know the analoge Olympus Pen F 18 x 24 mm, made in 1963 ? It had a standard 38 mm optic, terrible thing much too "long". Its little sister the Pen EE with a 28 mm, she was a beauty.
For Hasselblad 500 C/M some prefered a set of three optics: 50 mm, 80 mm and the 150 mm plus a small extension tube
Some did not like the 80 mm; a 60 mm or 100 mm thought to be nicer.
Today there is a crazy competition, who has got the shortest and who has got the longest optic. Do not forget to make photographs.
Take my advice. Read the story here below and forget it. Go to a decent photoshop and hold the camera and optics in your hand.