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A258433 Primes with repdigit indices (in decimal). 2
2, 3, 5, 7, 11, 13, 17, 19, 23, 31, 79, 137, 193, 257, 317, 389, 457, 523, 607, 1399, 2239, 3119, 4019, 4973, 5903, 6907, 7907, 8933, 19583, 30911, 42473, 54581, 66889, 79357, 92003, 104723, 117763, 252233, 393191, 538259, 686671, 836833, 989999, 1144153, 1299689, 1456667, 3080969, 4767181, 6495109, 8251153 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Elements of this sequence are the first 9 primes, then the 11th, 22nd, 33rd, ... , 99th, 111th, 222nd, etc. This is a somewhat remarkable sequence because of certain digital coincidences (see Prime Curios links).

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..153

Andrew Booker, The Nth Prime Page

Prime Curios!, 989999

Prime Curios!, 640663963

Wikipedia, Repdigit

Wikipedia, Prime-counting function

FORMULA

a(n) = A000040(A010785(n)).

EXAMPLE

The first prime skipped is the 10th, 29, so that a(10)=31.  Then follows a(11)=79, a(12)=137, a(13)=193, etc.: The 22nd, 33rd, and 44th primes, and so on.

MATHEMATICA

Prime[#]&/@(FromDigits/@Flatten[Table[PadRight[{}, k, n], {k, 6}, {n, 9}], 1]) (* Harvey P. Dale, Mar 25 2019 *)

PROG

(PARI) a(n)=prime(10^((n+8)\9)\9*((n-1)%9+1)) \\ Charles R Greathouse IV, Jun 03 2015

CROSSREFS

Cf. A000040, A010785, A105581.

Sequence in context: A046501 A033875 A105581 * A262363 A050264 A075239

Adjacent sequences:  A258430 A258431 A258432 * A258434 A258435 A258436

KEYWORD

nonn,base

AUTHOR

James G. Merickel, May 29 2015

STATUS

approved

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Last modified June 25 07:53 EDT 2019. Contains 324347 sequences. (Running on oeis4.)