|
| |
|
|
A101966
|
|
Indices of primes in sequence defined by A(0) = 21, A(n) = 10*A(n-1) + 61 for n > 0.
|
|
0
| | |
|
|
|
OFFSET
| 1,2
|
|
|
COMMENTS
| Numbers n such that (250*10^n - 61)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 7 followed by digit 1 is prime.
Numbers corresponding to terms <= 935 are certified primes.
a(n) = A098960(n-1) - 1.
|
|
|
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
| 271 is prime, hence 1 is a term.
|
|
|
MAPLE
| Do[If[PrimeQ[(250*10^n-61)/9], Print[n]], {n, 1, 3250}] (Steinerberger)
|
|
|
PROG
| (PARI) a=21; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+61)
(PARI) for(n=0, 1500, if(isprime((250*10^n-61)/9), print1(n, ", ")))
|
|
|
CROSSREFS
| Cf. A000533, A002275, A098960.
a(n) = A098960(n) - 1.
Sequence in context: A100840 A140154 A073694 * A184536 A089574 A077207
Adjacent sequences: A101963 A101964 A101965 * A101967 A101968 A101969
|
|
|
KEYWORD
| nonn,hard,more
|
|
|
AUTHOR
| Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004
|
|
|
EXTENSIONS
| a(7) from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Jan 31 2006
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
|
| |
|
|
