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A062828
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a(n) = gcd(2n, n(n+1)/2).
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3
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1, 1, 6, 2, 5, 3, 14, 4, 9, 5, 22, 6, 13, 7, 30, 8, 17, 9, 38, 10, 21, 11, 46, 12, 25, 13, 54, 14, 29, 15, 62, 16, 33, 17, 70, 18, 37, 19, 78, 20, 41, 21, 86, 22, 45, 23, 94, 24, 49, 25, 102, 26, 53, 27, 110, 28, 57, 29, 118, 30, 61, 31, 126, 32, 65, 33, 134, 34, 69, 35, 142
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OFFSET
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1,3
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COMMENTS
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LINKS
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FORMULA
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a(4n+1) = 4n+1, a(4n+2) = 2n+1, a(4n+3) = 8n+6, a(4n+4) = 2n+2. - Ralf Stephan, Jun 10 2005
G.f.: x*(1 + x + 6*x^2 + 2*x^3 + 3*x^4 + x^5 + 2*x^6) / ( (x-1)^2*(1+x)^2*(x^2+1)^2 ). - R. J. Mathar, Jul 25 2013
a(n) = n*(2-(-1)^n-sin(n*Pi/2))/2.
a(n) = 2*a(n-4) - a(n-8). (End)
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MAPLE
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igcd(2*n, n*(n+1)/2) ;
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MATHEMATICA
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Table[GCD[2n, (n(n+1))/2], {n, 120}] (* or *) LinearRecurrence[ {0, 0, 0, 2, 0, 0, 0, -1}, {1, 1, 6, 2, 5, 3, 14, 4}, 120] (* Harvey P. Dale, Apr 09 2018 *)
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PROG
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(PARI) j=[]; for(n=1, 150, j=concat(j, gcd(2*n, n*(n+1)/2))); j
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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