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

Author

Amarnath Murthy, Mar 19 2002

Keywords

• nonn
• base

Examples

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

Links

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

Crossrefs

Cf. A068876, A030152.

Programs

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 *)

Extensions

More terms from Sascha Kurz, Mar 23 2002