A077786 - OEIS

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A077786

Numbers k such that (10^k - 1) - 4*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).

2

177, 225, 397, 1245, 8457, 20105, 111725

(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..7.

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

Makoto Kamada, Prime numbers of the form 99...99599...99

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A183186(n) + 1.

EXAMPLE

177 is a term because (10^177 - 1) - 4*10^88 = 99...99599...99.

MATHEMATICA

Do[ If[ PrimeQ[10^n - 4*10^Floor[n/2] - 1], Print[n]], {n, 3, 20200, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A278198 A164843 A268790 * A188537 A169641 A255786

Adjacent sequences: A077783 A077784 A077785 * A077787 A077788 A077789

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

EXTENSIONS

One more term from PWP table added by Patrick De Geest, Nov 05 2014

Name corrected by Jon E. Schoenfield, Oct 31 2018

STATUS

approved