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A078499 Two-prime decades. 1
20, 30, 50, 60, 80, 150, 160, 170, 230, 250, 260, 270, 280, 330, 340, 350, 370, 380, 400, 440, 490, 500, 520, 540, 560, 570, 590, 600, 650, 670, 700, 730, 750, 760, 910, 940, 970, 990, 1010, 1100, 1120, 1150, 1180, 1210, 1220, 1230, 1270, 1280, 1290, 1320 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

select(t -> nops(select(isprime, [t+1, t+3, t+7, t+9]))=2, [seq(i, i=10..10^4, 10)]); # Robert Israel, Feb 05 2019

PROG

(PARI) decade2(n1, n2) = { if(n1==0, n1=10); forstep(x=n1, n2, 10, if(isprime(x+1) && isprime(x+3) && !isprime(x+7) && !isprime(x+9), print1(x" "); ); if(isprime(x+1) && isprime(x+7) && !isprime(x+3) && !isprime(x+9), print1(x" "); ); if(isprime(x+1) && isprime(x+9) && !isprime(x+3) && !isprime(x+7), print1(x" "); ); if(isprime(x+3) && isprime(x+7) && !isprime(x+1) && !isprime(x+9), print1(x" "); ); if(isprime(x+3) && isprime(x+9) && !isprime(x+1) && !isprime(x+7), print1(x" "); ); if(isprime(x+7) && isprime(x+9) && !isprime(x+1) && !isprime(x+3), print1(x" "); ); ); }

CROSSREFS

Sequence in context: A198471 A120145 A104048 * A066027 A256227 A142342

Adjacent sequences:  A078496 A078497 A078498 * A078500 A078501 A078502

KEYWORD

easy,nonn,base

AUTHOR

Cino Hilliard, Jan 04 2003

EXTENSIONS

Offset corrected by Robert Israel, Feb 05 2019

STATUS

approved

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Last modified January 17 14:57 EST 2020. Contains 330958 sequences. (Running on oeis4.)