|
Search: id:A061455
|
|
|
| A061455 |
|
Triangular numbers whose digit reversal is also a triangular number. |
|
+0
2
|
|
| 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
(list; graph; listen)
|
|
|
OFFSET
|
1,3
|
|
|
FORMULA
|
a(n)=A000217(k) and A004086(a(n))=A000217(j) for some k and j. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 02 2006
|
|
EXAMPLE
|
153 is in the sequence because (1) it is a triangular number and (2) the reversal 351 is also a trinagular number.
|
|
MAPLE
|
A000217 := proc(n) RETURN(n*(n+1)/2) ; end : isA000217 := proc(n) RETURN( issqr(1+8*n)) ; end: revdigs := proc(n) local resul, bas, i ; bas := convert(n, base, 10) ; resul :=0 ; for i from 1 to nops(bas) do resul := resul+bas[i]*10^(nops(bas)-i) ; od : RETURN(resul) ; end: A061455 := proc(nmax) local resul, n ; resul := [] ; for n from 0 to nmax do if isA000217(n) then if isA000217(revdigs(n)) then resul := [op(resul), n] ; fi ; fi ; end : RETURN(resul) ; end: A061455(30000000) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 02 2006
|
|
CROSSREFS
|
Cf. A000217.
Sequence in context: A081975 A160965 A069708 this_sequence A068071 A067269 A071299
Adjacent sequences: A061452 A061453 A061454 this_sequence A061456 A061457 A061458
|
|
KEYWORD
|
nonn,base,easy
|
|
AUTHOR
|
Amarnath Murthy (amarnath_murthy(AT)yahoo.com), May 03 2001
|
|
EXTENSIONS
|
More terms from Erich Friedman (efriedma(AT)stetson.edu), May 08 2001
Edited by N. J. A. Sloane (njas(AT)research.att.com), Aug 13 2008 at the suggestion of R. J. Mathar.
|
|
|
Search completed in 0.002 seconds
|
