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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.

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}] (from 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 April 19 14:42 EDT 2014. Contains 240761 sequences.