A100350 - OEIS

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A100350

Primes p such that p-2^k is a prime or semiprime for all k > 0 with 2^k < p.

7, 11, 13, 19, 23, 37, 41, 73

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OFFSET

1,1

COMMENTS

These are the primes in A100349. No others < 10^9; conjecture that this sequence is finite.

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

37 is here because 37-2, 37-4, 37-16 are semiprimes and 37-8, 37-32 are primes.

MATHEMATICA

SemiPrimeQ[n_Integer] := If[Abs[n]<2, False, (2==Plus@@Transpose[FactorInteger[Abs[n]]][[2]])]; lst={}; Do[k=1; While[n=Prime[i]; p=n-2^k; p>0 && (SemiPrimeQ[p] || PrimeQ[p]), k++ ]; If[p<=0, AppendTo[lst, n]], {i, 2, 1000}]; lst

CROSSREFS

Cf. A039669 (n such that n-2^k is prime), A100349 (n such that n-2^k is prime or semiprime), A100351 (n such that n-2^k is semiprime).

Sequence in context: A063911 A087489 A155488 * A084467 A245179 A297177

Adjacent sequences: A100347 A100348 A100349 * A100351 A100352 A100353

KEYWORD

more,nonn

AUTHOR

T. D. Noe, Nov 18 2004

STATUS

approved