A248165 - OEIS

A248165

a(1)=252; for n>=1, a(n+1) is the smallest palindromic 5-almost prime with a(n) as a central substring.

%I #29 Dec 02 2014 20:59:14

%S 252,92529,189252981,1218925298121,212189252981212,12121892529812121,

%T 8121218925298121218,781212189252981212187,1678121218925298121218761,

%U 216781212189252981212187612,22167812121892529812121876122,2221678121218925298121218761222

%N a(1)=252; for n>=1, a(n+1) is the smallest palindromic 5-almost prime with a(n) as a central substring.

%C The 5-almost primes are the numbers that are the product of exactly five (not necessarily distinct).

%e a(1) = 252 = 2*2*3*3*7;

%e a(2) = 92529 = 3*3*3*23*149.

%t d[n_]:= IntegerDigits[n]; t = {x = 252}; Do[i = 1; While[!PrimeOmega[y = FromDigits[Flatten[{z = d[i], d[x], Reverse[z]}]]]==5, i++]; AppendTo[t, x = y], {n, 13}]; t

%Y Cf. A014614, A247483, A247484, A248047.

%K nonn,base

%O 1,1

%A _Michel Lagneau_, Dec 01 2014