A027749 Take the list 1,2,3,4,... and replace each n with all d > 1 that divide n.

1, 2, 3, 2, 4, 5, 2, 3, 6, 7, 2, 4, 8, 3, 9, 2, 5, 10, 11, 2, 3, 4, 6, 12, 13, 2, 7, 14, 3, 5, 15, 2, 4, 8, 16, 17, 2, 3, 6, 9, 18, 19, 2, 4, 5, 10, 20, 3, 7, 21, 2, 11, 22, 23, 2, 3, 4, 6, 8, 12, 24, 5, 25, 2, 13, 26, 3, 9, 27, 2, 4, 7, 14, 28, 29, 2, 3, 5, 6, 10, 15, 30, 31, 2, 4, 8, 16, 32, 3, 11, 33, 2, 17, 34, 5, 7, 35

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy
• nice
• tabf

Comments

a(A002541(n)+1)=n; a(A002541(n)+2)=A020639(n+1). - Reinhard Zumkeller, Nov 22 2003

Seen as a triangle read by rows: T(1,1)=1 and T(n,k)=A027750(n,k+1) for n>1, 1<=k<A000005(n). - Reinhard Zumkeller, Oct 01 2012

Links

• Reinhard Zumkeller, Rows n = 1..250 of triangle, flattened

Crossrefs

Cf. A032741, A027750.

Programs

Haskell

a027749 n k = a027749_tabf !! (n-1) !! (k-1)
a027749_row n = a027749_tabf !! n
a027749_tabf = [1] : map tail (tail a027750_tabf)
-- Reinhard Zumkeller, Oct 01 2012, Oct 19 2011, Jul 11 2011

Mathematica

Join[{1},Flatten[Rest[Divisors[#]]&/@Range[40]]] (* Harvey P. Dale, Jun 28 2011 *)

Extensions

More terms from Scott Lindhurst (ScottL(AT)alumni.princeton.edu)

Keyword tabf added by Reinhard Zumkeller, Oct 01 2012