A068882 Triangular numbers with property that digits alternate in parity.

1, 3, 6, 10, 21, 36, 45, 78, 105, 210, 276, 325, 496, 561, 630, 703, 741, 903, 1830, 2145, 2701, 5050, 6105, 6903, 8385, 9870, 10585, 12561, 14365, 18145, 18721, 23436, 25878, 29890, 30381, 32385, 36585, 38503, 38781, 41616, 47278, 50721

Offset

1,2

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Example

1830 is a term as 1, 8, 3 and 0 have odd and even parity alternately.

Mathematica

altQ[n_] := n < 10 || Union[ Total /@ Partition[ Mod[ IntegerDigits@n, 2], 2, 1]] == {1}; t[n_] := n (n + 1)/2; Select[ t@ Range@ 400, altQ] (* Giovanni Resta, Aug 17 2018 *)

Crossrefs

Cf. A068876, A030152.

Sequence in context: A060179 A056411 A068855 * A076713 A299017 A136569

Adjacent sequences: A068879 A068880 A068881 * A068883 A068884 A068885

Keyword

nonn,base

Author

Amarnath Murthy, Mar 19 2002

Extensions

More terms from Sascha Kurz, Mar 23 2002

Status

approved