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A270974 Numbers k such that 7*10^k + 57 is prime. 3
1, 2, 3, 5, 6, 7, 12, 14, 19, 21, 27, 33, 60, 61, 91, 102, 535, 549, 614, 695, 709, 1014, 2448, 2519, 3464, 3511, 6348, 6841, 11009, 11177, 20754, 26610, 30651, 39246, 122294 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 0 followed by the digits 57 is prime (see Example section).

a(35) > 2*10^5.

LINKS

Table of n, a(n) for n=1..35.

Makoto Kamada, Search for 70w57.

EXAMPLE

3 is in this sequence because 7*10^3+57 = 7057 is prime.

Initial terms and primes associated:

a(1) = 1, 127;

a(2) = 2, 757;

a(3) = 3, 7057;

a(4) = 5, 700057;

a(5) = 6, 7000057;

a(6) = 7, 70000057, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[7*10^# + 57] &]

PROG

(PARI) lista(nn) = {for(n=1, nn, if(ispseudoprime(7*10^n + 57), print1(n, ", "))); } \\ Altug Alkan, Mar 27 2016

(MAGMA) [n: n in [1..500] | IsPrime(7*10^n + 57)]; // Vincenzo Librandi, Jul 03 2016

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929.

Sequence in context: A276692 A169829 A189208 * A039058 A046158 A070274

Adjacent sequences:  A270971 A270972 A270973 * A270975 A270976 A270977

KEYWORD

nonn,more

AUTHOR

Robert Price, Mar 27 2016

EXTENSIONS

a(35) from Robert Price, Jun 13 2019

STATUS

approved

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Last modified November 13 23:48 EST 2019. Contains 329106 sequences. (Running on oeis4.)