A121759 In decimal number system, take even digits of n with negative sign.

1, -2, 3, -4, 5, -6, 7, -8, 9, 10, 11, 8, 13, 6, 15, 4, 17, 2, 19, -20, -19, -22, -17, -24, -15, -26, -13, -28, -11, 30, 31, 28, 33, 26, 35, 24, 37, 22, 39, -40, -39, -42, -37, -44, -35, -46, -33, -48, -31, 50, 51, 48, 53, 46, 55, 44, 57, 42, 59, -60, -59, -62, -57, -64, -55, -66, -53, -68, -51, 70, 71, 68, 73, 66, 75, 64, 77, 62

Offset: 1

Author

Zak Seidov, Aug 20 2006

Keywords

• base
• sign
• nice
• look

Comments

See A121758. In decimal number system, take odd digits of n with negative sign.

a(A014261(n)) = A014261(n). - Reinhard Zumkeller, Nov 30 2007

Examples

			a(12) = 8 because 12 = 1*10^1 + 2*10^0 and a(12) = (-1)^(1+1)*1*10^1 + (-1)^(1+2)*2*10^0 = 10-2 = 8.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A121758.

Programs

Haskell

import Data.List (unfoldr)
a121759 = foldl f 0 . reverse . unfoldr d where
   d 0 = Nothing
   d x = Just $ swap $ divMod x 10
   f v d | even d = 10 * v - d
         | odd  d = 10 * v + d
-- Reinhard Zumkeller, Aug 01 2011

Mathematica

a[n_] := Total[MapIndexed[(-1)^(#1 + 1)*#1*10^(#2[[1]] - 1)&, Reverse[ IntegerDigits[n]]]]; Array[a, 78] (* Jean-François Alcover, Jun 20 2017 *)

Formula

If n = d(i)*10^(i-1), then a(n) = (-1)^(1+d(i))*d(i)*10^(i-1).

a(n) = -A121758(n).