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A133019
Product of n-th prime and n-th prime written backwards.
8
4, 9, 25, 49, 121, 403, 1207, 1729, 736, 2668, 403, 2701, 574, 1462, 3478, 1855, 5605, 976, 5092, 1207, 2701, 7663, 3154, 8722, 7663, 10201, 31003, 75007, 98209, 35143, 91567, 17161, 100147, 129409, 140209, 22801, 117907, 58843, 127087
OFFSET
1,1
COMMENTS
a(8) = 1729 is the second taxicab number, also called the Hardy-Ramanujan number (see A001235, A011541 and A133029).
LINKS
FORMULA
a(n) = A000040(n) * A004087(n)
EXAMPLE
a(8) = 1729 because the 8th prime is 19 and 19 written backwards is 91 and 19*91 = 1729.
MATHEMATICA
#*FromDigits[Reverse[IntegerDigits[#]]] & /@ Prime[Range[1, 50]] (* G. C. Greubel, Oct 02 2017 *)
#*IntegerReverse[#]&/@Prime[Range[40]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 29 2021 *)
PROG
(PARI) vector(60, n, prime(n)*subst(Polrev(digits(prime(n))), x, 10)) \\ Michel Marcus, Dec 17 2014
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Omar E. Pol, Oct 27 2007
STATUS
approved