|
| |
|
|
A077788
|
|
Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form 7*(10^a(n)-1)/9-10^[ a(n)/2 ].
|
|
1
| | |
|
|
|
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
| Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
Makoto Kamada, Prime numbers of the form 77...77677...77
Index entries for primes involving repunits.
|
|
|
FORMULA
| a(n) = 2*A183181(n)+1.
|
|
|
EXAMPLE
| a(n)=11 -> 7*(10^11-1)/9-10^5 = 77777677777.
|
|
|
MATHEMATICA
| Do[ If[ PrimeQ[(7*10^n - 9*10^Floor[n/2] - 7)/9], Print[n]], {n, 3, 30300, 2}] (from Robert G. Wilson v (rgwv(at)rgwv.com), Dec 16 2005)
|
|
|
CROSSREFS
| Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
Sequence in context: A075824 A108113 A111391 * A137018 A090771 A195572
Adjacent sequences: A077785 A077786 A077787 * A077789 A077790 A077791
|
|
|
KEYWORD
| more,nonn,base
|
|
|
AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com), Nov 16 2002.
|
| |
|
|
