A068650 Primes in which a string of 1's is sandwiched between two 3's.

313, 3111111111113, 311111111111113, 3111111111111111111111111111113, 311111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111113

Offset

1,1

Comments

The next term (a(6)) has 127 digits. - Harvey P. Dale, Dec 18 2022

Links

Harvey P. Dale, Table of n, a(n) for n = 1..8

Patrick De Geest, PDP Reference Table - 313.

Makoto Kamada, Prime numbers of the form 311...113.

Index entries for primes involving repunits.

Maple

a := 3:b := 1: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[10*FromDigits[PadRight[{3}, n, 1]]+3, {n, 2, 110}], PrimeQ] (* Harvey P. Dale, Dec 18 2022 *)

Crossrefs

Cf. A068645-A068651, A056251, A082704.

Sequence in context: A261818 A083997 A164772 * A106156 A286289 A219961

Adjacent sequences: A068647 A068648 A068649 * A068651 A068652 A068653

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