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A077796 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form 7*(10^a(n)-1)/9+2*10^[ a(n)/2 ]. 1
3, 5, 17, 39, 41, 425, 561, 1775, 2043, 11031, 16233, 23705 (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.

a(13) > 2*10^5. - Robert Price, Jan 19 2016

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..12.

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

Makoto Kamada, Prime numbers of the form 77...77977...77

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A183183(n)+1.

EXAMPLE

a(n)=17 -> 7*(10^17-1)/9+2*10^8 = 77777777977777777.

MATHEMATICA

Do[ If[ PrimeQ[(7*10^n + 18*10^Floor[n/2] - 7)/9], Print[n]], {n, 3, 23800, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A148516 A148517 A148518 * A241249 A067062 A148519

Adjacent sequences:  A077793 A077794 A077795 * A077797 A077798 A077799

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

STATUS

approved

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Last modified June 30 02:44 EDT 2016. Contains 274304 sequences.