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A102014
Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 51 for n > 0.
2
0, 1, 3, 6, 9, 12, 13, 21, 22, 28, 37, 49, 52, 66, 103, 349, 375, 411, 1204, 1834, 2509, 2667, 6096, 8295, 14295, 43368, 127348, 142033
OFFSET
1,3
COMMENTS
Numbers n such that (120*10^n + 51)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 3 followed by digit 9 is prime.
Numbers corresponding to terms <= 411 are certified primes.
a(27) > 10^5. - Robert Price, Nov 15 2014
a(29) > 2*10^5. - Tyler Busby, Feb 01 2023
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102933(n) - 1. - Robert Price, Nov 15 2014
EXAMPLE
139 is prime, hence 1 is a term.
MAPLE
A102014:=n->`if`(isprime((120*10^n + 51)/9), n, NULL): seq(A102014(n), n=0..1000); # Wesley Ivan Hurt, Nov 15 2014
PROG
(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-51)
(PARI) for(n=0, 1500, if(isprime((120*10^n+51)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(25)-a(26) derived from A102933 by Robert Price, Nov 15 2014
a(27)-a(28) from Tyler Busby, Feb 01 2023
STATUS
approved