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A018928 Define {b(n)} by b(1)=3, b(n) (n >= 2) is smallest number such that b(1)^2+...+b(n)^2 = m^2 for some m and all b(i) are distinct. Sequence gives values of m. 6
3, 5, 13, 85, 157, 12325, 12461, 106285, 276341, 339709, 10363909, 17238541, 1936511509, 51335823965, 133473142309, 872709007405, 1574530008629, 667511933218429, 698925273030725, 707670964169285, 1839944506840141 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also: Begin with the least length of a Pythagorean Triangle (PT), a(1)=3. Then a(n) is the least hypotenuse of a PT which has a(n-1) as one of its legs. - Robert G. Wilson v, Mar 17 2014

LINKS

Robert G. Wilson v, Table of n, a(n) for n = 1..165  (first 100 terms from Lei Zhou)

MATHEMATICA

NextA018928[n_] := Block[{a = n^2, b, l, i, c, d, f}, b = Divisors[a]; l = Length[b]; i = l; While[i--; c = b[[i]]; d = a/c - (c - 1); (d <= 1) || EvenQ[d]]; f = (a/c + (c - 1) + 1)/2]; Table[If[i == 1, a = 3, a = NextA018928[a]]; a, {i, 1, 21}](* Lei Zhou, Feb 20 2014 *)

f[s_List] := Block[{x = s[[-1]]}, Append[s, Transpose[ Solve[ x^2 + y^2 == z^2 && y > 0 && z > 0, {y, z}, Integers]][[-1, 1, 2]]]]; lst = Nest[f, lst, 15] (* Robert G. Wilson v, Mar 17 2014 *)

CROSSREFS

Cf. A018929, A018930.

Sequence in context: A159293 A051901 A268021 * A239381 A180313 A053630

Adjacent sequences:  A018925 A018926 A018927 * A018929 A018930 A018931

KEYWORD

nonn

AUTHOR

Charles Reed (charles.reed(AT)bbs.ewgateway.org)

EXTENSIONS

More terms from David W. Wilson

STATUS

approved

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Last modified December 16 06:18 EST 2019. Contains 330016 sequences. (Running on oeis4.)