A068648 - OEIS

A068648

Primes in which a string of 8's is sandwiched between two 1's.

11, 181, 188888881, 188888888888881, 18888888888888888888888888888888888888881, 188888888888888888888888888888888888888888888888888888888888888888888888888888888888888888881

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OFFSET

1,1

COMMENTS

The next term -- a(7) -- has 129 digits. - Harvey P. Dale, Jul 08 2020

LINKS

Table of n, a(n) for n=1..6.

Patrick De Geest, PDP Reference Table - 181.

Makoto Kamada, Prime numbers of the form 188...881.

Index entries for primes involving repunits.

EXAMPLE

11 is also a member in which a string of 0 8's is there between two one's.

MAPLE

a := 1:b := 8:i := 1:for n from 0 to 500 do c := a+10*(10^n-1)/9*b+10^(n+1)*a; if(isprime(c)) then d[i] := c; i := i+1; end if; end do:q := seq(d[j], j=1..i-1);

MATHEMATICA

Select[Table[10FromDigits[PadRight[{1}, n, 8]]+1, {n, 100}], PrimeQ] (* Harvey P. Dale, Jul 08 2020 *)

CROSSREFS

Cf. A068645-A068651, A056249, A082702.

Sequence in context: A372279 A057618 A270663 * A209351 A287062 A215203

Adjacent sequences: A068645 A068646 A068647 * A068649 A068650 A068651

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Feb 28 2002

EXTENSIONS

More terms from Sascha Kurz, Mar 19 2002

Edited by Ray Chandler, Nov 04 2014

STATUS

approved