|
Search: id:A056244
|
|
|
| A056244 |
|
Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 21 for n > 0. |
|
+0
1
|
|
| 0, 1, 3, 5, 93, 159, 359, 1469, 2897, 3093, 3111, 15697, 17955, 42261
(list; graph; listen)
|
|
|
OFFSET
|
1,3
|
|
|
COMMENT
|
Numbers n such that (120*10^n - 21)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 3 followed by digit 1 is prime.
Numbers corresponding to terms <= 359 are certified primes. For numbers corresponding to terms >= 1469 see P. De Geest, PDP Reference Table.
a(n) = A082697(n-2) - 2 for n > 1.
|
|
REFERENCES
|
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
|
|
LINKS
|
P. De Geest, PDP Reference Table
Makoto Kamada, Factorizations of 133...331.
|
|
EXAMPLE
|
131 is prime, hence 1 is a term.
|
|
MATHEMATICA
|
Do[If[PrimeQ[(1*10^n + 3*(10^n - 1)/9)*10 + 1], Print[n]], {n, 1, 2500}]
|
|
PROGRAM
|
(PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+21)
(PARI) for(n=0, 1500, if(isprime((120*10^n-21)/9), print1(n, ", ")))
|
|
CROSSREFS
|
Cf. A000533, A002275, A082697.
Sequence in context: A107655 A133660 A057663 this_sequence A103081 A003112 A130187
Adjacent sequences: A056241 A056242 A056243 this_sequence A056245 A056246 A056247
|
|
KEYWORD
|
nonn,hard,more
|
|
AUTHOR
|
Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 18 2000
|
|
EXTENSIONS
|
More terms and additional comments from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
Edited by N. J. A. Sloane (njas(AT)research.att.com), Jun 15 2007
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
|
|
|
Search completed in 0.002 seconds
|
