A082699 -id:A082699 - cp's OEIS frontend

A068646 Primes in which a string of 5's is sandwiched between two 1's.

11, 151, 15551, 155555555555555555551, 155555555555555555555555555555551

Offset: 1

Amarnath Murthy, Feb 28 2002

The next term is too big to include. - Sascha Kurz, Mar 19 2002

			11 is also a member in which a string of 0 5's is there between two one's.

Patrick De Geest, PDP Reference Table - 151.
Makoto Kamada, Prime numbers of the form 155...551.
Index entries for primes involving repunits.

Cf. A068645-A068651, A056246, A082699.

a := 1:b := 5: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);

Select[Table[FromDigits[Join[PadRight[{1},n,5],{1}]],{n,500}],PrimeQ] (* Harvey P. Dale, Aug 08 2012 *)

More terms from Sascha Kurz, Mar 19 2002

Edited by Ray Chandler, Nov 04 2014

A056246 Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 41 for n > 0.

Original entry on oeis.org

0, 1, 3, 19, 31, 399, 561, 7015, 37683

Offset: 1

Robert G. Wilson v, Aug 18 2000

Numbers n such that (140*10^n - 41)/9 is a prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 1 is a prime.
Numbers corresponding to terms <= 561 are certified primes.

			151 is a prime, hence 1 is a term.

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Patrick De Geest, PDP Reference Table - 151.
Makoto Kamada, Prime numbers of the form 155...551.
Index entries for primes involving repunits.

Cf. A000533, A002275, A068646, A082699.

Select[Range[0, 2000], PrimeQ[(140 10^# - 41) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)

a=11;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+41)

for(n=0,1500,if(isprime((140*10^n-41)/9),print1(n,",")))

a(n) = A082699(n-1) - 2 for n > 1.

Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
Edited by N. J. A. Sloane, Jun 15 2007
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Added and updated a link, by Patrick De Geest, Nov 02 2014
Edited by Ray Chandler, Nov 04 2014

cp's OEIS Frontend

A068646 Primes in which a string of 5's is sandwiched between two 1's.

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