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A077786 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)-4*10^[ a(n)/2 ]. 1
177, 225, 397, 1245, 8457, 20105, 111725 (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..7.

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

Makoto Kamada, Prime numbers of the form 99...99599...99

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A183186(n)+1.

EXAMPLE

a(n)=177 -> (10^177-1)-4*10^88 = 99...99599...99.

MATHEMATICA

Do[ If[ PrimeQ[10^n - 4*10^Floor[n/2] - 1], Print[n]], {n, 3, 20200, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A278198 A164843 A268790 * A188537 A169641 A255786

Adjacent sequences:  A077783 A077784 A077785 * A077787 A077788 A077789

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

EXTENSIONS

Added one more term 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.