|
|
A101139
|
|
Indices of primes in sequence defined by A(0) = 71, A(n) = 10*A(n-1) + 31 for n > 0.
|
|
1
|
|
|
0, 3, 5, 6, 9, 15, 21, 30, 1314, 2063, 6149, 8706, 12251, 18609, 21629, 41711, 44807, 45420
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
Numbers n such that (670*10^n - 31)/9 is prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 4 followed by digit 1 is prime.
Some of the larger entries may only correspond to probable primes.
|
|
REFERENCES
|
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
74441 is prime, hence 3 is a term.
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[(670*10^# - 31)/9] &] (* Robert Price, Sep 28 2015 *)
|
|
PROG
|
(PARI) a=71; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+31)
(PARI) for(n=0, 1500, if(isprime((670*10^n-31)/9), print1(n, ", ")))
(Magma) [n: n in [0..1000] | IsPrime((670*10^n-31) div 9)]; // Vincenzo Librandi, Sep 29 2015
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,hard,more
|
|
AUTHOR
|
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004
|
|
EXTENSIONS
|
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
|
|
STATUS
|
approved
|
|
|
|