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A075705 Safe primes (A005385) (p and (p-1)/2 are primes) such that 6*p+1 is also prime. 1
5, 7, 11, 23, 47, 83, 107, 263, 347, 467, 503, 863, 887, 1283, 1487, 1823, 1907, 2027, 2063, 2447, 2903, 3203, 3623, 4007, 4127, 4547, 4703, 4787, 5387, 5807, 7523, 7703, 8147, 8423, 11423, 11483, 11807, 12107, 12227, 12647, 12983, 13043, 13163, 14087, 14207 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

David Consiglio, Jr. and T. D. Noe, Table of n, a(n) for n = 1..1000

EXAMPLE

47 is prime, so is (47-1)/2=23 and also 6*47+1=283; 83 is a prime, (83-1)/2=41 and 6*83+1=499, ...

MAPLE

ts_sg_var_pras := proc(nmax) local i, tren, atek; tren := 0: for i from 1 to nmax do atek := numtheory[safeprime](i): if (atek > tren) then if (isprime(atek)='true' and isprime(6*atek+1)='true') then tren := atek: fi; fi; od; end: seq(ts_sg_var_pras(i), i=1..3000);

MATHEMATICA

Select[Range[20000], PrimeQ[#] && PrimeQ[(#-1)/2] && PrimeQ[6#+1] &] (* T. D. Noe, Nov 07 2011 *)

Select[Prime[Range[1700]], And@@PrimeQ[{(#-1)/2, 6#+1}]&] (* Harvey P. Dale, Feb 28 2013 *)

CROSSREFS

Cf. A005384, A005385, A059455, A007693.

Sequence in context: A092307 A005385 A181602 * A249735 A218394 A067289

Adjacent sequences:  A075702 A075703 A075704 * A075706 A075707 A075708

KEYWORD

nonn

AUTHOR

Jani Melik, Oct 02 2002

STATUS

approved

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Last modified January 16 06:59 EST 2019. Contains 319188 sequences. (Running on oeis4.)