Does A4 equal PA4 Wikipedia say so..
PA series
PA4-based series Name mm × mm Ratio
PA0 840 × 1120 3:4
PA1 560 × 840 2:3
PA2 420 × 560 3:4
PA3 280 × 420 2:3
PA4 210 × 280 3:4
PA5 140 × 210 2:3
PA6 105 × 140 3:4
PA7 70 × 105 2:3
PA8 52 × 70 ≈3:4
PA9 35 × 52 ≈2:3
PA10 26 × 35 ≈3:4
A transitional size called PA4 (210 mm × 280 mm, 8¼ in × 11 in) was proposed for inclusion into the ISO 216 standard in 1975. It has the height of Canadian P4 paper (215 mm × 280 mm, about 8½ in × 11 in) and the width of international A4 paper (210 mm × 297 mm). The table to the right shows how this format can be generalized into an entire format series.
The PA formats did not end up in ISO 216, because the committee felt that the set of standardized paper formats should be kept to the minimum necessary. However, PA4 remains of practical use today. In landscape orientation, it has the same 4:3 aspect ratio as the displays of traditional TV sets, some computer displays and data projectors. PA4, with appropriate margins, is therefore a good choice as the format of presentation slides. At the same time, PA4 is the largest format that fits on both A4 and US/Canadian Letter paper without resizing.
PA4 is used today by many international magazines, because it can be printed easily on equipment designed for either A4 or US Letter.