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 A062828 GCD of 2n and n(n+1)/2. 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 Index entries for linear recurrences with constant coefficients, signature (0,0,0,2,0,0,0,-1). FORMULA 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 MAPLE A062828 := proc(n)     igcd(2*n, n*(n+1)/2) ; end proc: # R. J. Mathar, Jul 25 2013 MATHEMATICA 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 *) PROG (PARI) j=[]; for(n=1, 150, j=concat(j, gcd(2*n, n*(n+1)/2))); j (PARI) a(n)=if(n%2, n*if(n%4>2, 2, 1), n/2) \\ Charles R Greathouse IV, Jul 07 2013 CROSSREFS Sequence in context: A007320 A199734 A007321 * A124457 A258102 A309449 Adjacent sequences:  A062825 A062826 A062827 * A062829 A062830 A062831 KEYWORD easy,nonn AUTHOR Jason Earls, Jul 20 2001 STATUS approved

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Last modified October 16 20:35 EDT 2019. Contains 328103 sequences. (Running on oeis4.)