|
| |
|
|
A069702
|
|
Triangular numbers with internal digits also forming a triangular number.
|
|
2
|
|
|
|
105, 136, 210, 231, 300, 406, 435, 465, 561, 630, 666, 703, 861, 903, 1035, 2016, 2211, 2556, 3003, 3916, 4005, 5151, 6105, 6216, 6555, 6786, 8001, 8911, 9453, 10011, 10153, 19900, 20100, 20910, 23005, 28203, 39903, 41905, 46665, 48205
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
COMMENTS
|
Includes (2*10^(2*k)-10^k-1)/9 for every k, so the sequence is infinite. - Robert Israel, Aug 28 2018
|
|
|
LINKS
|
Giovanni Resta, Table of n, a(n) for n = 1..1000 (first 210 terms from Robert Israel)
|
|
|
EXAMPLE
|
3916 is a member as 3916 and 91 both are triangular.
|
|
|
MAPLE
|
filter:= proc(x) local t, m;
t:= floor(x/10);
m:= ilog10(t);
t:= t - floor(t/10^m)*10^m;
issqr(8*t+1)
end proc:
select(filter, [seq(x*(x+1)/2, x=14..1000)]); # Robert Israel, Aug 28 2018
|
|
|
MATHEMATICA
|
s=Select[Range[14, 400], IntegerQ[Sqrt[1+8FromDigits[Drop[Drop[IntegerDigits[ #(#+1)/2], 1], -1]]]]&]; s(s+1)/2
|
|
|
CROSSREFS
|
Cf. A077366.
Sequence in context: A267891 A097217 A115935 * A239589 A203614 A252069
Adjacent sequences: A069699 A069700 A069701 * A069703 A069704 A069705
|
|
|
KEYWORD
|
base,nonn
|
|
|
AUTHOR
|
Amarnath Murthy, Apr 06 2002
|
|
|
EXTENSIONS
|
Edited by Dean Hickerson, Apr 09 2002
Edited by Robert Israel, Aug 28 2018
|
|
|
STATUS
|
approved
|
| |
|
|
