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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..1000

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.

MAPLE

with(numtheory):

T:=proc(w) local x, y, z; x:=0; y:=w; for z from 1 to

ilog10(w)+1 do x:=10*x+(y mod 10); y:=trunc(y/10); od; x; end:

P:=proc(q) local n; for n from 1 to q do

print(ithprime(n)*T(ithprime(n))); od; end: P(10^3); # Paolo P. Lava, Dec 17 2014

MATHEMATICA

#*FromDigits[Reverse[IntegerDigits[#]]] & /@ Prime[Range[1, 50]] (* G. C. Greubel, Oct 02 2017 *)

PROG

(PARI) vector(60, n, prime(n)*subst(Polrev(digits(prime(n))), x, 10)) \\ Michel Marcus, Dec 17 2014

CROSSREFS

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

Sequence in context: A158183 A158184 A001255 * A326708 A028866 A146981

Adjacent sequences:  A133016 A133017 A133018 * A133020 A133021 A133022

KEYWORD

base,easy,nonn

AUTHOR

Omar E. Pol, Oct 27 2007

STATUS

approved

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Last modified January 27 09:09 EST 2020. Contains 331293 sequences. (Running on oeis4.)