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 A167220 Triangular numbers that remain triangular numbers when their reverse is added. 0
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS 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

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Last modified September 23 20:42 EDT 2021. Contains 347617 sequences. (Running on oeis4.)