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A003098 Palindromic triangular numbers.
(Formerly M2605)
18
0, 1, 3, 6, 55, 66, 171, 595, 666, 3003, 5995, 8778, 15051, 66066, 617716, 828828, 1269621, 1680861, 3544453, 5073705, 5676765, 6295926, 35133153, 61477416, 178727871, 1264114621, 1634004361, 5289009825, 6172882716, 13953435931 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Charles W. Trigg, Palindromic Triangular Numbers, J. Rec. Math., 6 (1973), 146-147.

David Wells, The Penguin Dictionary of Curious and Interesting Numbers, p. 73 (Rev. ed. 1997)

LINKS

T. D. Noe, Table of n, a(n) for n = 1..148 (from P. De Geest)

P. De Geest, Palindromic Triangulars

MATHEMATICA

palQ[n_]:=Module[{idn=IntegerDigits[n]}, idn==Reverse[idn]]; Select[ Accumulate[ Range[200000]], palQ]  (* Harvey P. Dale, Mar 23 2011 *)

Select[Accumulate[Range[0, 170000]], PalindromeQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 15 2019 *)

PROG

(PARI) list(lim)=my(v=List(), d); for(n=0, (sqrt(8*lim+1)-1)/2, d=digits(n*(n+1)/2); if(d==Vecrev(d), listput(v, n*(n+1)/2))); Vec(v) \\ Charles R Greathouse IV, Jun 23 2017

CROSSREFS

Cf. A008509, A002113, A000217.

Sequence in context: A032070 A066569 A051641 * A045914 A303351 A067610

Adjacent sequences:  A003095 A003096 A003097 * A003099 A003100 A003101

KEYWORD

nonn,base,easy,nice

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)