

A102020


Indices of primes in sequence defined by A(0) = 17, A(n) = 10*A(n1)  13 for n > 0.


1



0, 1, 4, 6, 18, 19, 27, 57, 249, 396, 7590, 32715, 70977, 83586
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OFFSET

1,3


COMMENTS

Numbers n such that (140*10^n + 13)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime.
Numbers corresponding to terms <= 396 are certified primes.
a(15) > 10^5.  Robert Price, Jan 17 2015


REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462467.


LINKS

Table of n, a(n) for n=1..14.
Makoto Kamada, Prime numbers of the form 155...557.
Index entries for primes involving repunits.


FORMULA

a(n) = A102937(n+1)  1.


EXAMPLE

157 is prime, hence 1 is a term.


PROG

(PARI) a=17; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a13)
(PARI) for(n=0, 1500, if(isprime((140*10^n+13)/9), print1(n, ", ")))


CROSSREFS

Cf. A000533, A002275, A102937.
Sequence in context: A309334 A263319 A062046 * A125133 A109310 A219190
Adjacent sequences: A102017 A102018 A102019 * A102021 A102022 A102023


KEYWORD

nonn,hard,more


AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwthaachen.de), Dec 28 2004


EXTENSIONS

7590 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(12)a(14) derived from A102937 by Robert Price, Jan 17 2015


STATUS

approved



