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 A242224 Triangular array T read by rows, T(n, k) = n*k*(gcd(n,k)+2)/gcd(n,k)^2. 1
 3, 6, 4, 9, 18, 5, 12, 8, 36, 6, 15, 30, 45, 60, 7, 18, 12, 10, 24, 90, 8, 21, 42, 63, 84, 105, 126, 9, 24, 16, 72, 12, 120, 48, 168, 10, 27, 54, 15, 108, 135, 30, 189, 216, 11, 30, 20, 90, 40, 14, 60, 210, 80, 270, 12, 33, 66, 99, 132, 165, 198, 231, 264, 297, 330, 13 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Described in the CNRS link as a puzzle where op(n,k) is defined by: op(n,n)=n+2, op(n,k)=op(k,n) and op(n,n+k)/op(n,k)=(n+k)/k. If gcd(n,k)+2 is replaced by gcd(n,k), then triangle A051173 is obtained. LINKS Indranil Ghosh, Rows 1..100 of triangle, flattened Ana Rechtman, Mai, 1er défi, Images des Mathématiques, CNRS, 2014 (in French). See also Comments, Images des Mathématiques, CNRS, 2014. EXAMPLE Triangle begins:    3;    6,  4;    9, 18,  5;   12,  8, 36,  6;   15, 30, 45, 60,  7;   18, 12, 10, 24, 90,  8;   ... MATHEMATICA t[n_, k_] := n*k*(GCD[n, k] +2)/GCD[n, k]^2; Table[ t[n, k], {n, 12}, {k, n}] // Flatten (* Robert G. Wilson v, Jan 21 2018 *) PROG (PARI) tabl(nn) = {for (n=1, nn, for (k=1, n, print1(n*k*(gcd(n, k)+2)/gcd(n, k)^2, ", "); ); print(); ); } CROSSREFS Sequence in context: A083349 A065230 A316478 * A294671 A275985 A163294 Adjacent sequences:  A242221 A242222 A242223 * A242225 A242226 A242227 KEYWORD nonn,tabl AUTHOR Michel Marcus, May 08 2014 STATUS approved

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Last modified January 22 23:50 EST 2022. Contains 350504 sequences. (Running on oeis4.)