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 A097101 Numbers n that are the hypotenuse of exactly 7 distinct integer-sided right triangles, i.e., n^2 can be written as a sum of two squares in 7 ways. 24
 325, 425, 650, 725, 845, 850, 925, 975, 1025, 1275, 1300, 1325, 1445, 1450, 1525, 1690, 1700, 1825, 1850, 1950, 2050, 2175, 2225, 2275, 2425, 2525, 2535, 2550, 2600, 2650, 2725, 2775, 2825, 2873, 2890, 2900, 2925, 2975 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Comment from R. J. Mathar, Feb 26 2008, edited by Zak Seidov May 12 2008: (Start) There are nonsquares x which can be written as a sum of 2 nonzero squares in exactly 7 different ways and which are by definition not in this sequence. 203125 = (125*sqrt(13))^2 is the first example: 203125 = 625 + 202500 = 10404 + 192721 = 18225 + 184900= 22500 + 180625= 62500 + 140625= 69169 + 133956= 84100 + 119025. The second and third examples are 265625 = (125*sqrt(17))^2 and 406250=(125*sqrt(26))^2. (End) If m is a term, then 2*m and p*m are terms where p is any prime of the form 4k+3. - Ray Chandler, Dec 30 2019 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..10000 FORMULA Equals {n: A025426(n^2)=7}. EXAMPLE Example supplied by R. J. Mathar, Feb 26 2008: The smallest number that can be written as a sum of two nonzero squares in 7 different ways is 105625 = 325^2: 1296 + 104329 = 105625 = 325^2 6400 + 99225 = 105625 = 325^2 8281 + 97344 = 105625 = 325^2 15625 + 90000 = 105625 = 325^2 27225 + 78400 = 105625 = 325^2 38025 + 67600 = 105625 = 325^2 41616 + 64009 = 105625 = 325^2. MATHEMATICA r[a_]:={b, c}/.{ToRules[Reduce[0

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Last modified January 19 12:48 EST 2020. Contains 331049 sequences. (Running on oeis4.)