|
Search: id:A077367
|
|
|
| A077367 |
|
Triangular numbers whose external digits form a triangular number. Or triangular number whose MSD and LSD form a triangular number. |
|
+0
5
|
|
| 0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 190, 231, 435, 465, 595, 666, 1035, 1225, 1275, 1485, 1540, 1770, 1830, 2211, 2278, 2628, 2701, 3486, 3916, 4005, 4095, 4465, 5565, 5995, 6216, 6786, 9591, 10440, 10585, 11175, 11325, 11935, 12090
(list; graph; listen)
|
|
|
OFFSET
|
1,3
|
|
|
MATHEMATICA
|
T[n_] := n*(n + 1)/2; tQ[n_] := IntegerQ[Sqrt[8n + 1]]; f2[n_] := Block[{id = IntegerDigits[n]}, If[Length[id] < 3, Return[True]]; tQ[FromDigits[{First[id], Last[id]}]]]; Select[Array[T, 160, 0], f2] (*Chandler*)
|
|
CROSSREFS
|
Cf. A077366, A077368.
Sequence in context: A025738 A078256 A025731 this_sequence A077366 A077368 A069693
Adjacent sequences: A077364 A077365 A077366 this_sequence A077368 A077369 A077370
|
|
KEYWORD
|
base,easy,nonn
|
|
AUTHOR
|
Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 06 2002
|
|
EXTENSIONS
|
Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 28 2007
|
|
|
Search completed in 0.002 seconds
|
