A091791 Least multiple of n such that the n-th partial concatenation is a multiple of the n-th odd number (i.e., 2n-1).

1, 2, 15, 20, 25, 6, 91, 80, 99, 170, 88, 60, 325, 350, 225, 512, 646, 540, 114, 60, 672, 704, 460, 696, 675, 78, 135, 560, 493, 2010, 589, 992, 2145, 1768, 35, 900, 2072, 1900, 3159, 2680

Offset

1,2

Links

Table of n, a(n) for n=1..40.

Example

3 divides 12, 5 divides 1215, 7 divides 121520 etc.

Maple

A055642 := proc(n) ilog10(n)+ 1; end: Lcat := proc(L) local resul, i ; resul := op(1, L) ; for i from 2 to nops(L) do resul := resul*10^A055642(op(i, L))+op(i, L) ; od ; RETURN(resul) ; end: A091791 := proc(nmax) local a, k, n ; a := [1] ; for n from 2 to nmax do k :=1 ; while Lcat([op(a), k*n]) mod (2*n-1) <> 0 do k := k+1 ; od ; a := [op(a), k*n] ; od; a ; end: A091791(40); # R. J. Mathar, Jul 20 2007

Crossrefs

Cf. A091792.

Sequence in context: A194542 A076646 A076617 * A281660 A244324 A143660

Adjacent sequences: A091788 A091789 A091790 * A091792 A091793 A091794

Keyword

base,nonn

Author

Amarnath Murthy, Feb 18 2004

Extensions

More terms from R. J. Mathar, Jul 20 2007

Status

approved