|
Search: id:A101728
|
|
|
| A101728 |
|
Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 31 for n > 0. |
|
+0
1
|
|
| 5, 20, 21, 23, 50, 80, 131, 164, 620, 1449, 3423, 5978
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
Numbers n such that (410*10^n + 31)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.
Numbers corresponding to terms <= 620 are certified primes.
|
|
REFERENCES
|
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
|
|
LINKS
|
Makoto Kamada, Factorizations of near-repdigit numbers.
|
|
EXAMPLE
|
4555559 is prime, hence 5 is a term.
|
|
PROGRAM
|
(PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-31)
(PARI) for(n=0, 1500, if(isprime((410*10^n+31)/9), print1(n, ", ")))
|
|
CROSSREFS
|
Cf. A000533, A002275.
a(n) = A102993(n) - 1.
Sequence in context: A093482 A030696 A098047 this_sequence A053240 A034123 A088973
Adjacent sequences: A101725 A101726 A101727 this_sequence A101729 A101730 A101731
|
|
KEYWORD
|
nonn,hard,more
|
|
AUTHOR
|
Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
|
|
EXTENSIONS
|
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
|
|
|
Search completed in 0.002 seconds
|
