A248165 a(1)=252; for n>=1, a(n+1) is the smallest palindromic 5-almost prime with a(n) as a central substring.

252, 92529, 189252981, 1218925298121, 212189252981212, 12121892529812121, 8121218925298121218, 781212189252981212187, 1678121218925298121218761, 216781212189252981212187612, 22167812121892529812121876122, 2221678121218925298121218761222

Offset: 1

Author

Michel Lagneau, Dec 01 2014

Keywords

• nonn
• base

Comments

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

Examples

			a(1) = 252 = 2*2*3*3*7;
a(2) = 92529 = 3*3*3*23*149.
		

Crossrefs

Cf. A014614, A247483, A247484, A248047.

Programs

Mathematica

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