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A350990
Triangular numbers that are palindromes in base 3.
5
0, 1, 10, 28, 91, 820, 7381, 65341, 66430, 597871, 1633528, 5380840, 48339028, 48427561, 139386556, 435848050, 1178284240, 3529890253, 3922632451, 32614707700, 35296517971, 35303692060, 101891588176, 292358957446, 295883935480, 317733228541, 859413596320, 2649105942220
OFFSET
1,3
COMMENTS
This sequence is infinite since A000217((3^k-1)/2) is a term for all k >= 0 (Trigg, 1971).
LINKS
Charles W. Trigg, Problem 3413, Problem Department, School Science and Mathematics, Vol. 71, No. 9 (1971), p. 843; Solution to Problem 3413, by Bob Prielipp, Vol. 72, No. 4 (1972), p. 358.
Charles W. Trigg, Infinite sequences of palindromic triangular numbers, The Fibonacci Quarterly, Vol. 12, No. 2 (1974), pp. 209-212.
EXAMPLE
10 is a term since 10 = A000217(4) is a triangular number and also a palindromic number in base 3: 10 = 101_3.
28 is a term since 28 = A000217(7) is a triangular number and also a palindromic number in base 3: 36 = 1001_3.
MATHEMATICA
t[n_] := n*(n + 1)/2; Select[t /@ Range[0, 3*10^5], PalindromeQ[IntegerDigits[#, 3]] &]
CROSSREFS
Intersection of A000217 and A014190.
The ternary version of A003098.
Sequence in context: A076712 A116973 A352180 * A264579 A003665 A332432
KEYWORD
nonn,base
AUTHOR
Amiram Eldar, Jan 28 2022
STATUS
approved