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A127698 Sum of n-th triangular number and its reversal. 1
0, 2, 6, 12, 11, 66, 33, 110, 99, 99, 110, 132, 165, 110, 606, 141, 767, 504, 342, 281, 222, 363, 605, 948, 303, 848, 504, 1251, 1010, 969, 1029, 1190, 1353, 726, 1190, 666, 1332, 1010, 888, 867, 848, 1029, 1212, 1595, 1089, 6336, 2882, 9339, 7887, 6446 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Gupta states in Prime Curios: "The smallest odd prime which can be represented as sum of a triangular number and its reverse, i.e., 10 + 01 = 11."

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..14141

G. L. Honaker, Jr. and Chris Caldwell, eds., 11.

FORMULA

a(n) = A000217(n) + A004086(A000217(n)).

EXAMPLE

a(0) = 0 + 0 = 0.

a(1) = 1 + 1 = 2 is the even prime.

a(4) = 10 + 1 = 11 is an odd prime.

a(5) = 15 + 51 = 66 = A000217(10).

a(19) = 190 + 91 = 281 is an odd prime.

a(24) = 300 + 3 = 303.

a(35) = 630 + 36 = 666 = A000217(36).

MAPLE

a:= n-> (p-> parse(cat(p, "+", seq(p[-i],

       i=1..length(p)))))(""||(n*(n+1)/2)):

seq(a(n), n=0..60);  # Alois P. Heinz, Jun 19 2016

MATHEMATICA

rev[n_] := FromDigits@ Reverse@ IntegerDigits@ n; t[n_] := n (n + 1)/2; Table[t@ n + rev@ t@ n, {n, 0, 49}] (* Giovanni Resta, Jun 19 2016 *)

#+IntegerReverse[#]&/@Accumulate[Range[0, 50]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 20 2016 *)

CROSSREFS

Cf. A000217, A004086.

Sequence in context: A329654 A009230 A069491 * A130503 A278232 A074385

Adjacent sequences:  A127695 A127696 A127697 * A127699 A127700 A127701

KEYWORD

base,easy,look,nonn

AUTHOR

Jonathan Vos Post, Apr 03 2007

EXTENSIONS

Edited by Giovanni Resta, Jun 19 2016

STATUS

approved

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Last modified August 5 15:41 EDT 2021. Contains 346477 sequences. (Running on oeis4.)