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A078687 Number of x>=0 such that prime(n)-2^x is prime. 5
0, 1, 1, 2, 2, 2, 1, 3, 2, 1, 2, 2, 1, 2, 2, 1, 1, 3, 2, 2, 2, 2, 3, 1, 1, 2, 2, 2, 2, 2, 0, 3, 1, 4, 0, 2, 2, 1, 3, 2, 1, 4, 1, 1, 2, 4, 2, 1, 3, 3, 1, 1, 3, 0, 2, 2, 1, 3, 2, 1, 2, 3, 1, 1, 2, 2, 0, 0, 2, 2, 3, 1, 2, 0, 2, 3, 1, 2, 2, 2, 1, 3, 1, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 1, 2, 3, 0, 1, 3, 2, 1, 1, 3, 1, 4 (list; graph; refs; listen; history; internal format)
OFFSET

1,4

LINKS

T. D. Noe, Table of n, a(n) for n=1..1000

FORMULA

a(A049084(A065381(n)))=0, a(A049084(A065380(n)))=1; A118953(n)<=a(n); a(n)=A109925(A000040(n)). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), May 07 2006

EXAMPLE

prime(17)=59 and only 59-2^3 = 53 is prime hence a(17)=1

PROG

(PARI) a(n)=sum(i=0, floor(log(prime(n))/log(2)), if(isprime(prime(n)-2^i), 1, 0))

CROSSREFS

Sequence in context: A083898 A078314 A068322 * A133138 A194326 A194290

Adjacent sequences:  A078684 A078685 A078686 * A078688 A078689 A078690

KEYWORD

nonn

AUTHOR

Benoit Cloitre (benoit7848c(AT)orange.fr), Dec 17 2002

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Last modified February 14 10:43 EST 2012. Contains 205614 sequences.