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 A128487 Irregular array where n-th row is the positive integers < n which are coprime to exactly one distinct prime divisor of n. 3
 1, 1, 2, 1, 3, 1, 2, 3, 4, 2, 3, 4, 1, 2, 3, 4, 5, 6, 1, 3, 5, 7, 1, 2, 4, 5, 7, 8, 2, 4, 5, 6, 8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 2, 3, 4, 8, 9, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 2, 4, 6, 7, 8, 10, 12, 3, 5, 6, 9, 10, 12, 1, 3, 5, 7, 9, 11, 13, 15, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,3 COMMENTS Number of terms in n-th row is A126080(n). Row 1 has zero terms, so the first listed row is row 2. LINKS Table of n, a(n) for n=2..97. EXAMPLE Concerning row 12: 1,5,7,11 don't appear because they are each coprime to 2 AND 3 (the distinct prime divisors of 12). 6 doesn't appear because it is coprime to neither prime dividing 12. The row consists of 2,3,4,8,9,10 because each term is coprime to exactly one prime divisor of 12 (i.e., is coprime to 2 or 3, but not to both). First few rows of the triangle: 1; 1, 2; 1, 3; 1, 2, 3, 4; 2, 3, 4; 1, 2, 3, 4, 5, 6; 1, 3, 5, 7; 1, 2, 4, 5, 7, 8; 2, 4, 5, 6, 8; 1, 2, 3, 4, 5, 6, 7, 8, 9, 10; 2, 3, 4, 8, 9, 10; 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12; ... PROG (PARI) row(n) = my(f=factor(n)); Vec(select(x->(x==1), vector(n-1, j, sum(k=1, #f~, gcd(j, f[k, 1]) == 1)), 1)); tabf(nn) = for (n=1, nn, print(row(n)); \\ Michel Marcus, Oct 25 2017 CROSSREFS Cf. A126080, A128488. Sequence in context: A293248 A096107 A329585 * A056609 A014673 A346704 Adjacent sequences: A128484 A128485 A128486 * A128488 A128489 A128490 KEYWORD nonn,tabf AUTHOR Leroy Quet, Mar 04 2007 EXTENSIONS More terms from R. J. Mathar, Oct 08 2007 STATUS approved

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Last modified August 3 19:29 EDT 2024. Contains 374909 sequences. (Running on oeis4.)