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A248047 a(1)=88; for n>=1, a(n+1) is the smallest palindromic 4-almost prime with a(n) as a central substring.

%I A248047 #28 Dec 02 2014 20:58:09
%S A248047 88,1881,218812,12188121,1121881211,111218812111,51112188121115,
%T A248047 1511121881211151,815111218812111518,78151112188121115187,
%U A248047 1781511121881211151871,917815111218812111518719,59178151112188121115187195,9591781511121881211151871959
%N A248047 a(1)=88; for n>=1, a(n+1) is the smallest palindromic 4-almost prime with a(n) as a central substring.
%C A248047 The 4-almost primes are the numbers that are the product of exactly four (not necessarily distinct) primes.
%e A248047 a(1)=88=2*2*2*11;
%e A248047 a(2)=1881=3*3*11*19;
%e A248047 a(3)=218812=2*2*11*4973.
%t A248047 d[n_]:=IntegerDigits[n]; t = {x = 88}; Do[i = 1; While[!PrimeOmega[y = FromDigits[Flatten[{z = d[i], d[x], Reverse[z]}]]]==4, i++]; AppendTo[t, x = y], {n, 14}]; t
%Y A248047 Cf. A014613, A247483, A247484.
%K A248047 nonn,base
%O A248047 1,1
%A A248047 _Michel Lagneau_, Dec 01 2014