A133019 Product of n-th prime and n-th prime written backwards.

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

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.

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

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

Sequence in context: A158184 A001255 A357754 * A376746 A326708 A028866

Adjacent sequences: A133016 A133017 A133018 * A133020 A133021 A133022

Keyword

base,easy,nonn

Author

Omar E. Pol, Oct 27 2007

Status

approved