A099190
Numbers n such that 8*10^n-7 is prime.
Original entry on oeis.org
1, 3, 5, 6, 10, 12, 13, 39, 48, 54, 64, 82, 147, 148, 360, 399, 1638, 1876, 2146, 2194, 15789, 23074, 38466, 68400
Offset: 1
73, 7993, 799993, 7999993, etc. are primes.
-
Do[ If[ PrimeQ[8*10^n - 7], Print[n]], {n, 10000}]
-
is(n)=ispseudoprime(8*10^n-7) \\ Charles R Greathouse IV, Feb 20 2017
A169830
Numbers k such that 2*reverse(k) - k = 1.
Original entry on oeis.org
1, 73, 793, 7993, 79993, 799993, 7999993, 79999993, 799999993, 7999999993, 79999999993, 799999999993, 7999999999993, 79999999999993, 799999999999993, 7999999999999993, 79999999999999993, 799999999999999993, 7999999999999999993, 79999999999999999993, 799999999999999999993
Offset: 1
-
k = 1; lst = {}; fQ[n_] := 2 FromDigits@ Reverse@ IntegerDigits@n == 1 + n; While[k < 10^8, If[fQ@k, Print@k; AppendTo[lst, k]]; k++ ]; lst (* Robert G. Wilson v, Jun 01 2010 *)
Rest@ CoefficientList[Series[x (1 + 62 x)/((1 - x) (1 - 10 x)), {x, 0, 20}], x] (* or *)
Table[If[n == 1, 1, FromDigits@ Join[{7}, ConstantArray[9, n - 2], {3}]], {n, 20}] (* or *)
LinearRecurrence[{11, -10}, {1, 73}, 20] (* Michael De Vlieger, Feb 12 2017 *)
-
isok(n) = 2*fromdigits(Vecrev(digits(n))) - n == 1; \\ Michel Marcus, Feb 12 2017
A101849
Indices of primes in sequence defined by A(0) = 37, A(n) = 10*A(n-1) + 27 for n > 0.
Original entry on oeis.org
0, 1, 13, 19, 29, 43, 65, 259, 871, 8845, 26743, 57505, 98471, 106891
Offset: 1
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
397 is prime, hence 1 is a term.
- Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
-
Select[Range[0, 1000], PrimeQ[(360*10^# - 27)/9] &] (* Robert Price, Mar 17 2015 *)
-
a=37;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+27)
-
for(n=0,1500,if(isprime((360*10^n-27)/9),print1(n,",")))
8845 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Showing 1-3 of 3 results.
Comments