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A087636 Number of n-digit lunar primes. 7

%I

%S 0,18,81,1539,20457,242217,2894799,33535839,381591711

%N Number of n-digit lunar primes.

%C Although a(1) through a(6) are divisible by 9, a(7) is not.

%H D. Applegate, <a href="/A087061/a087061.txt">C program for lunar arithmetic and number theory</a>

%H D. Applegate, M. LeBrun and N. J. A. Sloane, <a href="http://arxiv.org/abs/1107.1130">Dismal Arithmetic</a>, arxiv:1107.1130 [math.NT], July 2011. [Note: we have now changed the name from "dismal arithmetic" to "lunar arithmetic" - the old name was too depressing]

%H D. Applegate, M. LeBrun, N. J. A. Sloane, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL14/Sloane/carry2.html">Dismal Arithmetic</a>, J. Int. Seq. 14 (2011) # 11.9.8.

%H <a href="/index/Di#dismal">Index entries for sequences related to dismal (or lunar) arithmetic</a>

%o (PARI) A87636=[]; A087636(n)={while(#A87636<n,A87636=concat(A87636,0)); !A87636[n] && A87636[n]=sum(k=10^(n-1),10^n-1,is_A087097(k)); A87636[n]} \\ Store results in array A87636 to avoid re-calculation. - _M. F. Hasler_, Nov 15 2018

%Y Cf. A087062 (lunar product), A087097 (lunar primes), A087638 (partial sums).

%K nonn,base,more

%O 1,2

%A Marc LeBrun and _N. J. A. Sloane_, Oct 26 2003

%E a(6)-a(9) from _David Applegate_, Nov 07 2003

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Last modified June 13 00:57 EDT 2021. Contains 344980 sequences. (Running on oeis4.)