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A118479 Least n-digit prime which is also a twin prime and Sophie Germain prime. 3
3, 11, 179, 1019, 10091, 100361, 1000211, 10001399, 100001651, 1000002359, 10000003001, 100000026569, 1000000000061, 10000000019759, 100000000018109, 1000000000029911, 10000000000013741, 100000000000004381 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..100

EXAMPLE

3 and 5 twin primes and 2*3+1=7 prime, so 3 is first of twin primes and Sophie Germain prime, least prime like this of one digit, so a(1)=3

11 and 13 twin primes ans 2*11+1=23 prime, so 11 first of twin primes and Sophie Germain prime, least prime like this with two digits, so a(2)=11

MATHEMATICA

f[n_] := Block[{k = 10^(n - 1)}, While[ !PrimeQ[k] || !PrimeQ[k + 2] || !PrimeQ[2k + 1], k++ ]; k]; Array[f, 18] (* Robert G. Wilson v, May 13 2006 *)

lndp[n_]:=Module[{p=NextPrime[10^n]}, While[NoneTrue[p+{2, -2}, PrimeQ] || !PrimeQ[2p+1], p=NextPrime[p]]; p]; Array[ lndp, 20, 0] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 06 2019 *)

CROSSREFS

Cf. A001359, A005384.

Sequence in context: A006485 A003115 A053888 * A103836 A284704 A081484

Adjacent sequences:  A118476 A118477 A118478 * A118480 A118481 A118482

KEYWORD

nonn,base

AUTHOR

Pierre CAMI, May 05 2006

EXTENSIONS

Edited by Robert G. Wilson v, May 13 2006

STATUS

approved

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Last modified April 23 06:38 EDT 2021. Contains 343201 sequences. (Running on oeis4.)