A167220 Triangular numbers that remain triangular numbers when their reverse is added.

0, 3, 15, 630, 1830, 2346, 4371, 5253, 5460, 19110, 98346, 478731, 519690, 1216020, 10669890, 266539416, 311737965, 377836305, 4375193196, 5476282185, 57391534206, 3361994343645, 7631474751153, 9750146019741, 43606139789376, 1199784486145710

Offset

1,2

Links

Table of n, a(n) for n=1..26.

Formula

{A000217(i) : A000217(i)+A004158(i) in A000217}. [R. J. Mathar, Oct 31 2009]

Example

2346 is a triangular number and 2346 + 6432 = 8778 is also a triangular number.

Maple

read("transforms"): A000217 := proc(n) n*(n+1)/2 ; end proc:
isA000217 := proc(n) issqr( 1+8*n) ; end proc:
isA167220 := proc(n) R := digrev(n) ; return isA000217(n) and isA000217(n+R) ; end:
for n from 0 to 30000 do T := A000217(n) ; if isA167220(T) then printf("%d, ", T) ; end if; od: # R. J. Mathar, Oct 31 2009

Crossrefs

Sequence in context: A338293 A267096 A217449 * A296939 A077399 A219122

Adjacent sequences: A167217 A167218 A167219 * A167221 A167222 A167223

Keyword

base,nonn

Author

Claudio Meller, Oct 30 2009

Extensions

5 more terms from R. J. Mathar, Oct 31 2009

a(21)-a(26) from Donovan Johnson, Apr 26 2011

Status

approved