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A077778 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1) - 7*10^[ a(n)/2 ]. 1
3, 17, 19, 705, 1061, 1395, 2631, 3837, 5749, 11753, 13537, 125877, 269479 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Prime versus probable prime status and proofs are given in the author's table.

REFERENCES

C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

LINKS

Table of n, a(n) for n=1..13.

Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)

Makoto Kamada, Prime numbers of the form 99...99299...99

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A115073(n)+1.

EXAMPLE

a(n)=17 -> (10^17-1)-7*10^8 = 99999999299999999.

MATHEMATICA

Do[ If[ PrimeQ[10^n - 7*10^Floor[n/2] - 1], Print[n]], {n, 3, 14600, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.

Sequence in context: A018750 A177208 A147845 * A273420 A022127 A273448

Adjacent sequences:  A077775 A077776 A077777 * A077779 A077780 A077781

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

EXTENSIONS

Added two more terms from PWP table, by Patrick De Geest, Nov 05 2014

STATUS

approved

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Last modified September 23 20:33 EDT 2017. Contains 292391 sequences.