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A101958
Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 13 for n > 0.
1
0, 3, 6, 11, 29, 93, 177, 195, 563, 1800, 3519, 3537, 8232, 35160, 37404, 42329, 70050, 90791
OFFSET
1,2
COMMENTS
Numbers n such that (220*10^n - 13)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 4 followed by digit 3 is prime.
Numbers corresponding to terms <= 563 are certified primes.
With changed signs, expansion of sinh(atan(x)).
Next term after 3537 is greater than 5000. - Ryan Propper, Jun 16 2005
a(19) > 10^5. - Robert Price, Mar 16 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102953(n) - 1.
EXAMPLE
24443 is prime, hence 3 is a term.
PROG
(PARI) a=23; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a+13)
(PARI) for(n=0, 2000, if(isprime((220*10^n-13)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004
EXTENSIONS
2 more terms from Ryan Propper, Jun 16 2005
8232 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007
a(14)-a(18) derived from A102953 by Robert Price, Mar 16 2015
STATUS
approved