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A146760 Last prime subtrahend at 10^n in A146759. 4
5, 61, 997, 9929, 97283, 999983, 9999973, 99897341, 999999929, 9993948257, 99999999761, 999999999989, 9999516957181, 99999999999929, 999999999999989, 9999999999998857, 99999429057832259, 999999999999999989, 9999990391470218071 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It is not necessary to compute A146759 to compute this sequence. a(n) is the largest prime p<=10^n such that c(p)-p is also a prime, where c(p) is the smallest cube exceeding p. - Sean A. Irvine, Mar 27 2013

LINKS

Sean A. Irvine, Table of n, a(n) for n = 1..150

EXAMPLE

A(2)=61 because 61 is the 7th and last prime subtrahend under 10^3.

PROG

(UBASIC)

10 'cu less pr are prime

20 N=1:O=1:C=1

30 A=3:S=sqrt(N):if N>10^3 then print N, C-1:stop

40 B=N\A

50 if B*A=N then 100

60 A=A+2

70 if A<=S then 40

80 R=O^3:Q=R-N

90 if N<R and N=prmdiv(N) and Q=prmdiv(Q) then if Q>1 print R; N; Q; C:N=N+2:C=C+1:goto 30

100 N=N+2:if N<R then 30:else O=O+1:goto 80

CROSSREFS

Cf. A146756, A146757, A146759.

Sequence in context: A012167 A162167 A134282 * A294024 A083082 A213110

Adjacent sequences:  A146757 A146758 A146759 * A146761 A146762 A146763

KEYWORD

easy,nonn

AUTHOR

Enoch Haga, Nov 02 2008

EXTENSIONS

More terms from Sean A. Irvine, Mar 27 2013

STATUS

approved

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Last modified August 9 18:32 EDT 2020. Contains 336326 sequences. (Running on oeis4.)