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%I #32 Nov 17 2019 01:20:31
%S 5,4,4,2,25,27,24,18,190,172,155,151,1424,1280,1243,1225,10924,10512,
%T 10399,10207,92015,88693,87149,85844,788498,767916,744036,736193,
%U 6891972,6755263,6698063,6699928,61960057,60731724,58734513,57667571,552358972,540945484,533119350,531667127
%N The number of palindromic primes leading and ending with 1, 3, 7 or 9 -- in sequence -- of length 2*ceiling(n/4)+1.
%C The way the sequence is titled/written is to give uniformity to the numbers considered. Thus, a(4k-3), a(4k-2), a(4k-1) and a(4k) are the counts of the (2k+1)-digit palprimes beginning with 1, 3, 7 and 9, respectively, leaving out consideration of the primes 2, 3, 5, 7 and 11 (the first 5 terms of A002385) as not really of type as far as this sequence is concerned.
%e If one wants, say, the number of 13-digit palindromic primes with 7 as the leading digit, then what one wants is the 3rd term after 5 groups of 4, or the 23rd, which is a(23)=87149. The palprimes corresponding to a(1)=5 are 101, 131, 151, 181 and 191.
%Y Cf. A002385, A220344, A220349.
%K nonn,base
%O 1,1
%A _James G. Merickel_, Dec 08 2012
%E a(37)-a(40) added by _James G. Merickel_, Dec 30 2012