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Product of n-th prime and n-th prime written backwards.
8

%I #15 Feb 27 2024 03:00:45

%S 4,9,25,49,121,403,1207,1729,736,2668,403,2701,574,1462,3478,1855,

%T 5605,976,5092,1207,2701,7663,3154,8722,7663,10201,31003,75007,98209,

%U 35143,91567,17161,100147,129409,140209,22801,117907,58843,127087

%N Product of n-th prime and n-th prime written backwards.

%C a(8) = 1729 is the second taxicab number, also called the Hardy-Ramanujan number (see A001235, A011541 and A133029).

%H Paolo P. Lava, <a href="/A133019/b133019.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A000040(n) * A004087(n)

%e a(8) = 1729 because the 8th prime is 19 and 19 written backwards is 91 and 19*91 = 1729.

%t #*FromDigits[Reverse[IntegerDigits[#]]] & /@ Prime[Range[1, 50]] (* _G. C. Greubel_, Oct 02 2017 *)

%t #*IntegerReverse[#]&/@Prime[Range[40]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 29 2021 *)

%o (PARI) vector(60, n, prime(n)*subst(Polrev(digits(prime(n))), x, 10)) \\ _Michel Marcus_, Dec 17 2014

%Y Cf. A001235, A004087, A011541, A061205, A067563, A067087, A133029. Prime numbers: A000040.

%K base,easy,nonn

%O 1,1

%A _Omar E. Pol_, Oct 27 2007