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A117587 Numbers k such that 2^prime(k) - prime(k)^2 is prime. 1
3, 4, 7, 8, 16, 23, 49, 89, 331, 497, 1122, 11222 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No more terms below 5000. - Giovanni Resta, Apr 03 2006

p is a prime element of the sequence A072180 iff pi(p) is a term of A117587. So since 119087 is a prime term of A072180, pi(119087)= 11222 is in the sequence. - Farideh Firoozbakht, Dec 08 2006

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

4 is in the sequence because the 4th prime is 7 and 2^7 - 7^2 = 79 is a prime.

MAPLE

a:=proc(n) if isprime(2^ithprime(n)-ithprime(n)^2) then n else fi end: seq(a(n), n=1..400); # Emeric Deutsch, Apr 06 2006

MATHEMATICA

Select[Range[1200], PrimeQ[2^# - #^2] &@ Prime@ # &] (* Michael De Vlieger, Feb 02 2019 *)

PROG

(PARI) for(i=1, 100, if(isprime(2^prime(i)-prime(i)^2), print1(i, ", ")))

CROSSREFS

Cf. A072180.

Sequence in context: A050069 A219019 A306612 * A244930 A130420 A214096

Adjacent sequences:  A117584 A117585 A117586 * A117588 A117589 A117590

KEYWORD

hard,more,nonn

AUTHOR

Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Apr 03 2006

EXTENSIONS

3 more terms from Giovanni Resta, Apr 03 2006

One more term from Farideh Firoozbakht, Dec 08 2006

STATUS

approved

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Last modified April 5 12:34 EDT 2020. Contains 333241 sequences. (Running on oeis4.)