A280720 - OEIS

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A280720

For p = prime(n), number of iterations of the function f(x) = 5x + 2 that leave p prime.

0, 1, 0, 1, 0, 2, 0, 3, 0, 0, 2, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 2, 0, 0, 2, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 2, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 2, 0, 0, 2, 0, 0, 0, 4, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0

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OFFSET

1,6

COMMENTS

Records are a(1) = 0 [p = 2], a(2) = 1 [p = 3], a(6) = 2 [p = 13], a(8) = 3 [p = 19], a(74) = 4 [p = 373], a(12656) = 6 [p = 135859], a(1165346) = 7 [p = 18235423], a(1659004) = 8 [p = 26588257], a(5386789) = 9 [p = 93112729], .... - Charles R Greathouse IV, Jan 12 2017

LINKS

John Cerkan, Table of n, a(n) for n = 1..10001

MATHEMATICA

Table[Length@ NestWhileList[5 # + 2 &, Prime@ n, PrimeQ] - 2, {n, 120}] (* Michael De Vlieger, Jan 09 2017 *)

PROG

(PARI) a016873(n) = 5*n+2

a(n) = my(p=prime(n), i=0); while(1, if(!ispseudoprime(a016873(p)), return(i), p=a016873(p); i++))

CROSSREFS

Cf. A016873, A023217, A023252, A023283, A023313, A023341, A084958, A249573.

Sequence in context: A085246 A268726 A035182 * A245964 A141700 A345228

Adjacent sequences: A280717 A280718 A280719 * A280721 A280722 A280723

KEYWORD

nonn

AUTHOR

Felix Fröhlich, Jan 07 2017

STATUS

approved