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A068882 Triangular numbers with property that digits alternate in parity. 8
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 28 16:37 EDT 2022. Contains 354119 sequences. (Running on oeis4.)