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A265629 Numbers k > 0 such that 10^(k+4) - 23 is prime. 2
7, 13, 19, 31, 157, 761, 3469, 6883, 27677 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers k such that '9977' appended to k times the digit 9 is prime.

Up to a(8) the terms themselves are primes.

LINKS

Table of n, a(n) for n=1..9.

FORMULA

a(n) mod 2 = 1. - Altug Alkan, Dec 14 2015

EXAMPLE

7 appears because 99999999977 ('9' concatenated 7 times and prepended to '9977') is prime.

MAPLE

A265629:=n->`if`(isprime((10^(n+4) - 23), n, NULL): seq(A265629(n), n=1..1000)

MATHEMATICA

Select[ Range[10^3], PrimeQ[10^(# + 4) - 23] &]

PROG

(MAGMA) [n: n in [1..200] | IsPrime((10^(n+4) - 23)];

(PARI) is(n)=isprime(10^(n+4) - 23)

CROSSREFS

Cf. A260903.

Sequence in context: A240971 A023255 A122482 * A283191 A048375 A198035

Adjacent sequences:  A265626 A265627 A265628 * A265630 A265631 A265632

KEYWORD

nonn,base,more

AUTHOR

Mikk Heidemaa, Dec 11 2015

STATUS

approved

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Last modified January 22 09:39 EST 2022. Contains 350481 sequences. (Running on oeis4.)