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A240882 Numbers n such that n - 4*k^2 is a prime for all k > 0 with k^2 < n/4. 0
6, 7, 9, 11, 15, 21, 23, 27, 33, 35, 47, 77, 83, 143, 167, 227, 437 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No other terms with n < 1000000. - Colin Barker, Apr 14 2014

LINKS

Table of n, a(n) for n=1..17.

EXAMPLE

21 is in this sequence because 21-4*1^2 = 17 and  21-4*2^2 = 5 are both prime.

PROG

(PARI) isOK(n) = k=1; until(k^2>=n/4, if(!isprime(n-4*k^2), return(0)); k++); 1;

for(n=3, 1000000, if(isOK(n), print1(n, ", "))) \\ Colin Barker, Apr 14 2014

CROSSREFS

Cf. A240842.

Sequence in context: A175221 A094010 A100348 * A241266 A095908 A094698

Adjacent sequences:  A240879 A240880 A240881 * A240883 A240884 A240885

KEYWORD

nonn,more

AUTHOR

Ilya Lopatin and Juri-Stepan Gerasimov, Apr 14 2014

EXTENSIONS

One missing term and one additional term from Colin Barker, Apr 14 2014

STATUS

approved

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Last modified February 17 20:06 EST 2018. Contains 299296 sequences. (Running on oeis4.)