

A183180


Numbers n such that (7*10^(2n+1)  18*10^n  7)/9 is prime.


1



0, 1, 7, 13, 58, 129, 253, 1657, 2244, 2437, 7924, 9903, 11899, 18157, 18957, 23665
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OFFSET

1,3


COMMENTS

a(16) > 10^5.  Robert Price, Jun 23 2017
0 could be considered part of this sequence since the formula evaluates to 5 which is a degenerate form of the nearrepdigit palindrome 777...77577...777 with 0 occurrences of the digit 7.  Robert Price, Jun 23 2017


REFERENCES

C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 199697, pp. 19.


LINKS

Table of n, a(n) for n=1..16.
Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
Makoto Kamada, Prime numbers of the form 77...77577...77
Index entries for primes involving repunits.


FORMULA

a(n) = (A077785(n)  1)/2.


MATHEMATICA

Do[If[PrimeQ[(7*10^(2n + 1)  18*10^n  7)/9], Print[n]], {n, 3000}]


PROG

(PARI) is(n)=ispseudoprime((7*10^(2*n+1)18*10^n7)/9) \\ Charles R Greathouse IV, Jun 13 2017


CROSSREFS

Cf. A004023, A077775A077798, A107123A107127, A107648, A107649, A115073, A183174A183187.
Sequence in context: A015441 A255286 A253210 * A133664 A143794 A159198
Adjacent sequences: A183177 A183178 A183179 * A183181 A183182 A183183


KEYWORD

nonn,base


AUTHOR

Ray Chandler, Dec 28 2010


EXTENSIONS

a(15) from Robert Price, Jun 23 2017


STATUS

approved



