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A155882 Smallest positive prime number such that a(n)-2n is also prime, a(n) < a(n+1), and the differences a(n)-2n must increase with n. 1
5, 11, 17, 31, 41, 53, 61, 83, 89, 103, 131, 137, 157, 167, 179, 199, 227, 233, 271, 281, 293, 307, 317, 331, 367, 383, 401, 409, 431, 439, 463, 503, 509, 547, 557, 563, 577, 599, 619, 643, 653, 661, 673, 701, 709, 733, 821, 829, 859, 887, 911, 967, 983, 991 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subtracting from a(1) twice n=1 gives 5-2=3, which is a prime number; subtracting from a(2) twice n=2 gives 11-4=7, which is a prime number; subtracting from a(3) twice n=3 gives 17-6=11, which is a prime number; subtracting from a(4) twice n=4 gives 31-8=23, which is a prime number; etc.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000

MAPLE

b:= proc(n) option remember; global a; a(n); b(n) end: a:= proc(n) option remember; local m; global b; if n=1 then b(1):= 3; 5 else for m from a(n-1)+2 by 2 while not (isprime(m) and (b(n-1)<m-2*n) and isprime (m-2*n)) do od; b(n):= m-2*n; m fi end: seq (a(n), n=1..100); # Alois P. Heinz, Feb 05 2009

CROSSREFS

Cf. A020484, A108184 (for the differences a(n)-2n).

Sequence in context: A068072 A136292 A088046 * A087373 A155030 A030468

Adjacent sequences: A155879 A155880 A155881 * A155883 A155884 A155885

KEYWORD

base,easy,nonn

AUTHOR

Eric Angelini, Jan 29 2009

EXTENSIONS

Corrected definition and more terms from Alois P. Heinz, Feb 05 2009

STATUS

approved

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Last modified December 2 11:09 EST 2022. Contains 358493 sequences. (Running on oeis4.)