A084008 a(n) = T(n) concatenated with reverse(T(n)) divided by 11, where T(n) is the n-th triangular number.

0, 1, 3, 6, 91, 141, 192, 262, 333, 414, 505, 606, 717, 829, 9591, 10911, 12421, 13941, 15561, 17281, 19092, 21012, 23032, 25152, 27273, 29593, 31923, 34443, 36964, 39594, 42324, 45154, 48075, 51015, 54145, 57276, 60606, 63937, 67377, 70917, 74548, 78288

Offset

0,3

Links

Table of n, a(n) for n=0..41.

Example

a(12) = 7887/11 = 717.

Maple

a:= n-> (t-> parse(cat(t, (s-> seq(s[-i], i=1..length(s)))(""||t)))/11)(n*(n+1)/2):
seq(a(n), n=0..50);  # Alois P. Heinz, Nov 17 2018

Mathematica

r[n_] := FromDigits[Join[IntegerDigits[n], Reverse[IntegerDigits[n]]]]; Do[k = n*(n+1)/2; Print[r[k]/11], {n, 0, 50}] (* Ryan Propper, Sep 26 2005 *)
f[n_]:=Module[{idn=IntegerDigits[n]}, FromDigits[Join[idn, Reverse[ idn]]] /11]; f/@Accumulate[Range[0, 40]] (* Harvey P. Dale, Sep 15 2011 *)

Crossrefs

Cf. A000217, A004086.

Sequence in context: A211896 A299433 A036286 * A092680 A101574 A082980

Adjacent sequences: A084005 A084006 A084007 * A084009 A084010 A084011

Keyword

base,nonn

Author

Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 23 2003

Extensions

More terms from Ryan Propper, Sep 26 2005

Status

approved