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A183179 Numbers n such that 7*(10^(2n+1)-1)/9 - 3*10^n is prime. 2
2, 3, 6, 23, 36, 69, 561, 723, 3438, 4104, 9020, 13977, 19655, 32400 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Original name: Numbers n such that (7*10^(2n+1)-27*10^n-7)/9 is prime.
a(15) > 10^5. - Robert Price, Nov 23 2015
REFERENCES
C. Caldwell and H. Dubner, The near repdigit primes A(n-k-1)B(1)A(k), especially 9(n-k-1)8(1)9(k), Journal of Recreational Mathematics, Volume 28, No. 1, 1996-97, pp. 1-9.
LINKS
Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
FORMULA
a(n) = (A077781(n)-1)/2.
MATHEMATICA
Do[If[PrimeQ[(7*10^(2n + 1) - 27*10^n - 7)/9], Print[n]], {n, 3000}]
PROG
(PARI) for(n=1, 1e3, if(ispseudoprime((7*10^(2*n+1)-27*10^n-7)/9), print1(n, ", "))) \\ Altug Alkan, Nov 23 2015
CROSSREFS
Sequence in context: A000616 A233217 A261963 * A018300 A317973 A361333
KEYWORD
nonn,base
AUTHOR
Ray Chandler, Dec 28 2010
EXTENSIONS
a(14) from Robert Price, Nov 23 2015
STATUS
approved

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Last modified March 29 01:36 EDT 2024. Contains 371264 sequences. (Running on oeis4.)