A247484 a(1)=8; for n>=1, a(n+1) is the smallest palindromic 3-almost prime with a(n) as a central substring.

8, 282, 52825, 4528254, 145282541, 2214528254122, 122145282541221, 51221452825412215, 7512214528254122157, 15751221452825412215751, 7157512214528254122157517, 371575122145282541221575173, 93715751221452825412215751739, 3937157512214528254122157517393

Offset: 1

Author

Michel Lagneau, Dec 01 2014

Keywords

• nonn
• base

Comments

The 3-almost primes are the numbers that are the product of exactly three (not necessarily distinct) primes.

Examples

			a(1) = 8 = 2*2*2;
a(2) = 282 = 2*3*47;
a(3) = 52825 = 5*5*2113;
a(4) = 4528254 = 2*3*754709.
		

Crossrefs

Cf. A014612, A247483.

Programs

Mathematica

d[n_]:=IntegerDigits[n];t = {x = 8}; Do[i = 1; While[!PrimeOmega[y = FromDigits[Flatten[{z = d[i], d[x], Reverse[z]}]]]==3, i++]; AppendTo[t, x = y], {n, 13}]; t