A146760 Last prime subtrahend at 10^n in A146759.

5, 61, 997, 9929, 97283, 999983, 9999973, 99897341, 999999929, 9993948257, 99999999761, 999999999989, 9999516957181, 99999999999929, 999999999999989, 9999999999998857, 99999429057832259, 999999999999999989, 9999990391470218071

Offset: 1

Author

Enoch Haga, Nov 02 2008

Keywords

• easy
• nonn

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

Examples

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

Links

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

Crossrefs

Cf. A146756, A146757, A146759.

Programs

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 N1 print R;N;Q;C:N=N+2:C=C+1:goto 30
100 N=N+2:if N
				

Extensions

More terms from Sean A. Irvine, Mar 27 2013