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A100952 Numbers that cannot be written as p*q+r with three distinct primes p, q and r. 1
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 24, 30, 36, 42, 60 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A100951(a(n)) = 0;

Conjecture: the sequence is complete.

A weaker conjecture: every integer greater than 60 (or some larger value based on further search) may be partitioned into a prime p and a semiprime qr, where the prime p is bounded by log(min(q,r)). Chen (1978) showed that all sufficiently large even numbers are the sum of a prime and the product of at most two primes. Zumkeller's conjecture effectively extends this from "even" to both even and odd integers. - Jonathan Vos Post, Nov 25 2004

Conjecture: Every positive integer can be represented as p*q-r with distinct primes p, q, r. - Zak Seidov, Aug 28 2012

REFERENCES

Chen, J.-R. "On the Representation of a Large Even Number as the Sum of a Prime and the Product of at Most Two Primes, II." Sci. Sinica 21, 421-430, 1978.

LINKS

Table of n, a(n) for n=1..21.

EXAMPLE

A100949(60) = #{11+7*7, 5+5*11, 3+3*19, 2+2*29} = 4, but A100951(60) = 0 as in each partition only 2 primes are used, therefore 60 is a term.

CROSSREFS

Cf. A100949, A100951.

Sequence in context: A117296 A096503 A055238 * A303332 A030477 A178859

Adjacent sequences:  A100949 A100950 A100951 * A100953 A100954 A100955

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Nov 23 2004

STATUS

approved

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Last modified August 7 04:39 EDT 2020. Contains 336274 sequences. (Running on oeis4.)