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 A081521 Triangle read by rows: row n contains n terms in increasing order, relatively prime to n, whose sum is a multiple of n and such that the row contains the smallest possible subset of consecutive numbers starting with 1. 5
 1, 1, 3, 1, 4, 7, 1, 3, 5, 7, 1, 2, 3, 6, 8, 1, 5, 7, 11, 13, 17, 1, 2, 3, 4, 5, 8, 12, 1, 3, 5, 7, 9, 11, 13, 15, 1, 2, 4, 5, 7, 8, 10, 13, 22, 1, 3, 7, 9, 11, 13, 17, 19, 21, 29, 1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 20 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The "smallest set of n distinct numbers" is not a well-defined term in the definition. Why is row 5 "1,2,3,6,8" but not "1,2,4,6,7"? Why is row 7 "1,2,3,4,5,8,12" but not "1,2,4,5,6,8,9"? - R. J. Mathar, Nov 12 2006 LINKS EXAMPLE Triangle begins:   1;   1, 3;   1, 4, 7;   1, 3, 5,  7;   1, 2, 3,  6,  8;   1, 5, 7, 11, 13, 17;   1, 2, 3,  4,  5,  8, 12;   ... PROG (PARI) row(n) = {my(m=n*(n-1)/2, v); forstep(k=m+n/(2-n%2), oo, n, v=List([]); for(i=2, k-m, if(gcd(n, i)==1, listput(v, i))); if(#v>n-2, forsubset([#v, n-1], w, if(r=1+sum(i=1, n-1, v[w[i]])==k, return(concat(1, vector(n-1, i, v[w[i]]))))))); } \\ Jinyuan Wang, May 24 2020 CROSSREFS Cf. A081522, A081523, A081524. Sequence in context: A170839 A049918 A028861 * A213224 A210218 A086273 Adjacent sequences:  A081518 A081519 A081520 * A081522 A081523 A081524 KEYWORD nonn,tabl,more AUTHOR Amarnath Murthy, Mar 27 2003 EXTENSIONS New definition proposed by Omar E. Pol, Mar 24 2008, in an attempt to answer R. J. Mathar's questions. Name corrected and more terms from Jinyuan Wang, May 24 2020 STATUS approved

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Last modified May 12 21:06 EDT 2021. Contains 343829 sequences. (Running on oeis4.)