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 A061455 Triangular numbers whose digit reversal is also a triangular number. 4
 0, 1, 3, 6, 10, 55, 66, 120, 153, 171, 190, 300, 351, 595, 630, 666, 820, 3003, 5995, 8778, 15051, 17578, 66066, 87571, 156520, 180300, 185745, 547581, 557040, 617716, 678030, 828828, 1269621, 1461195, 1680861, 1851850, 3544453, 5073705, 5676765, 5911641 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Jon E. Schoenfield, Table of n, a(n) for n = 1..162 (terms < 10^18) FORMULA a(n)=A000217(k) and A004086(a(n))=A000217(j) for some k and j. - R. J. Mathar, Jun 02 2006 EXAMPLE 153 is in the sequence because (1) it is a triangular number and (2) its reversal 351 is also a triangular number. MAPLE read("transforms"); isA000217 := proc(n) issqr(1+8*n) ; end proc: isA061455 := proc(n) isA000217(n) and isA000217(digrev(n)) ; end proc: for n from 0 to 60000 do T := A000217(n) ; if isA061455(T) then printf("%d, ", T) ; end if; end do: # R. J. Mathar, Dec 13 2010 MATHEMATICA TriangularNumberQ[k_] := If[IntegerQ[1/2 (Sqrt[1 + 8 k] - 1)], True, False]; Select[Range[0, 5676765], TriangularNumberQ[#] && TriangularNumberQ[FromDigits[Reverse[IntegerDigits[#]]]] &] (* Ant King, Dec 13 2010 *) PROG (PARI) isok(n) = ispolygonal(n, 3) && ispolygonal(fromdigits(Vecrev(digits(n))), 3); \\ Michel Marcus, Apr 14 2019 CROSSREFS Cf. A000217, A004086. Sequence in context: A081975 A160965 A069708 * A068071 A067269 A071299 Adjacent sequences:  A061452 A061453 A061454 * A061456 A061457 A061458 KEYWORD nonn,base,easy AUTHOR Amarnath Murthy, May 03 2001 EXTENSIONS More terms from Erich Friedman, May 08 2001 Edited by N. J. A. Sloane, Aug 13 2008 at the suggestion of R. J. Mathar STATUS approved

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Last modified January 18 16:27 EST 2020. Contains 331011 sequences. (Running on oeis4.)