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A018930
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a(1)=3; for n>1, a(n) is smallest positive integer such that a(1)^2+...+a(n)^2 = m^2 for some m.
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7
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3, 4, 12, 84, 132, 12324, 1836, 105552, 255084, 197580, 10358340, 13775220, 1936434780, 51299286012, 123205977516, 862441842612, 1310543298204, 667510076211780, 207181940072172, 110912831751840, 1698410314006284
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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f[n_]:=Module[{a={3}}, Do[AppendTo[a, First[y/. {ToRules[Reduce[{y^2+a.a == x^2, x>0, y>0}, {y, x}, Integers]]}]], {n-1}]; a]; f[21]//Timing (* Jean-François Alcover, Jan 26 2007 *)
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PROG
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(PARI) print1("3, "); s=9; for(n=1, 30, d=divisors(s); t=d[#d\2]; q=(s\t-t)/2; print1(q, ", "); s+=q^2); \\ Max Alekseyev, Nov 23 2012
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Charles Reed (charles.reed(AT)bbs.ewgateway.org)
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EXTENSIONS
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STATUS
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approved
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