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A175220 The fifth nonprimes after the primes. 1
10, 10, 12, 14, 18, 20, 24, 25, 28, 35, 36, 44, 48, 49, 52, 58, 65, 66, 74, 77, 78, 85, 88, 94, 104, 108, 110, 114, 115, 118, 133, 136, 143, 144, 155, 156, 162, 169, 172, 178, 185, 186, 198, 200, 203, 204, 216, 230, 234, 235, 238, 245, 246, 256, 262, 268, 275 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

From Robert Israel, Jul 05 2016: (Start)

For n>1, there are the following cases:

If prime(n)+2 and prime(n)+4 are composite, then a(n) = prime(n)+5.

If exactly one of prime(n)+2 and prime(n)+4 is prime, and prime(n)+6 is composite, then a(n) = prime(n) + 6.

Otherwise, a(n) = prime(n) + 7. (End)

LINKS

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

MAPLE

N:= 1000: # to get all entries <= N

Primes:= select(isprime, [2, seq(i, i=3..N+7, 2)]):

nprimes:= nops(Primes):

A[1]:= 10:

A[2]:= 10:

for i from 3 to nprimes-1 do

  p:= Primes[i];

  if p + 5 > N then break fi;

  if Primes[i+1] > p + 4 then A[i]:= p + 5

  elif (i = nprimes-1 or Primes[i+2] <> p+6) and p+6 <= N  then A[i]:= p + 6

  elif p+7 <= N then A[i]:= p + 7

  else break

  fi

od:

seq(A[j], j=1..i-1); # Robert Israel, Jul 05 2016

CROSSREFS

Sequence in context: A173198 A111381 A063660 * A272479 A167427 A227437

Adjacent sequences:  A175217 A175218 A175219 * A175221 A175222 A175223

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Mar 06 2010

STATUS

approved

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Last modified June 23 04:15 EDT 2021. Contains 345395 sequences. (Running on oeis4.)