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

1,1

Comments

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

Links

Table of n, a(n) for n=1..12.

Example

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

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

Crossrefs

Cf. A014614, A247483, A247484, A248047.

Sequence in context: A289293 A183507 A203385 * A289567 A179714 A109929

Adjacent sequences: A248162 A248163 A248164 * A248166 A248167 A248168

Keyword

nonn,base

Author

Michel Lagneau, Dec 01 2014

Status

approved