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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 ]. +0
1
3, 5, 17, 39, 41, 425, 561, 1775, 2043, 11031, 16233, 23705 (list; graph; listen)
OFFSET

1,1

COMMENT

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

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

Makoto Kamada, Factorizations of 77...77977...77

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 (rgwv(at)rgwv.com), Dec 16 2005)

CROSSREFS

Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A114633-A114647.

Sequence in context: A148516 A148517 A148518 this_sequence A067062 A148519 A148520

Adjacent sequences: A077793 A077794 A077795 this_sequence A077797 A077798 A077799

KEYWORD

nonn,base

AUTHOR

Patrick De Geest (pdg(AT)worldofnumbers.com), Nov 16 2002.

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Last modified December 13 23:45 EST 2009. Contains 170824 sequences.


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