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A278932 Numbers n such that n remains prime through 6 iterations of function f(x) = 2x + 1. 1
1122659, 2164229, 2329469, 10257809, 10309889, 12314699, 14030309, 14145539, 19099919, 23103659, 24176129, 28843649, 37088729, 38199839, 42389519, 49160099, 50785439, 52554569, 62800169, 68718059, 85864769, 88174049, 95831189, 105109139, 105388169 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n, 2*n+1, 4*n+3, 8*n+7, 16*n+15, 32*n+31, and 64*n+63 are primes.

a(n) == 29 (mod 30).

LINKS

Table of n, a(n) for n=1..25.

PROG

(PARI) a005408(n) = 2*n+1

count(n) = my(k=n, i=0); while(ispseudoprime(k), k=a005408(k); i++); i

is(n) = count(n) > 6 \\ Felix Fröhlich, Dec 05 2016

CROSSREFS

Subsequence of A007700, A023272, A023302, and A023330.

Sequence in context: A059121 A176194 A116175 * A059767 A069583 A109209

Adjacent sequences:  A278929 A278930 A278931 * A278933 A278934 A278935

KEYWORD

nonn

AUTHOR

John Cerkan, Dec 01 2016

STATUS

approved

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Last modified February 26 05:51 EST 2020. Contains 332277 sequences. (Running on oeis4.)