A162703 Palindromes in A005448.
1, 4, 15151, 45154, 66466, 92629, 98689, 4976794, 6424246, 648616846, 136287949782631, 479573060375974, 69465717171756496, 4345218593958125434, 42097537753535773579024, 58071646151315164617085, 6220959179720279719590226, 458122911526080625119221854
Offset: 1
Examples
T(99) + T(100) + T(101) = 15151. T(172) + T(173) + T(174) = 45154.
Links
- Patrick De Geest, Table of n, a(n) for n = 1..30
- Patrick De Geest, Palindromic Centered Polygonal Numbers
- Terry Trotter, Polygonal Numbers from the Wayback machine
Programs
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Mathematica
n = 1; lst = {}; While[n < 10^10, ctn = 3 n (n - 1)/2 + 1; id = IntegerDigits@ ctn; If[id == Reverse@id, AppendTo[lst, ctn]; Print[{n, ctn}]]; n++ ]; lst (* Robert G. Wilson v *)
Formula
a(n) = (3*m^2 - 3*m + 2)/2 or a(n) = (3*n^2 + 3*n + 2)/2 with n = m - 1.
Extensions
Edited and extended by R. J. Mathar and Robert G. Wilson v, Jul 13 2009
a(14)-a(17) from Donovan Johnson, Sep 29 2011
a(18)-a(30) from Patrick De Geest, May 23 2021
Comments