|
|
A077788
|
|
Numbers k such that 7*(10^k - 1)/9 - 10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).
|
|
2
|
|
|
|
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..9.
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
|
11 is a term because 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}] (* Robert G. Wilson v, Dec 16 2005 *)
|
|
CROSSREFS
|
Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
Sequence in context: A228951 A108113 A111391 * A339048 A137018 A182391
Adjacent sequences: A077785 A077786 A077787 * A077789 A077790 A077791
|
|
KEYWORD
|
more,nonn,base
|
|
AUTHOR
|
Patrick De Geest, Nov 16 2002
|
|
EXTENSIONS
|
Name corrected by Jon E. Schoenfield, Oct 31 2018
|
|
STATUS
|
approved
|
|
|
|