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A127698
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Sum of n-th triangular number and its reversal (leading zeros not truncated).
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0
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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; internal format)
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OFFSET
| 0,2
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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." Note that this is not the definition of digital reversal, R(n), which truncates leading zeros, used in A004086 and other sequences.
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REFERENCES
| Angell, I. O. and Godwin, H. J. "On Truncatable Primes." Math. Comput. 31, 265-267, 1977.
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LINKS
| Index entries for sequences related to truncatable primes
G. L. Honaker, Jr. and Chris Caldwell, eds., 11.
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FORMULA
| a(n) = A000217(n) + pseudoreversal(A000217(n)) where pseudoreversal(n) is the digital reversal with leading zeros left intact (not truncated).
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EXAMPLE
| a(0) = 0 + 0 = 0.
a(1) = 1 + 1 = 2 is the even prime.
a(4) = 10 + 01 = 11 is an odd prime.
a(5) = 15 + 51 = 66 = A000217(10).
a(19) = 190 + 091 = 281 is an odd prime.
a(24) = 300 + 003 = 303.
a(35) = 630 + 036 = 666 = A000217(36).
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CROSSREFS
| Cf. A000217, A004086.
Sequence in context: A145103 A009230 A069491 * A130503 A074385 A057340
Adjacent sequences: A127695 A127696 A127697 * A127699 A127700 A127701
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KEYWORD
| base,easy,nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 03 2007
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