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

88, 1881, 218812, 12188121, 1121881211, 111218812111, 51112188121115, 1511121881211151, 815111218812111518, 78151112188121115187, 1781511121881211151871, 917815111218812111518719, 59178151112188121115187195, 9591781511121881211151871959

Offset

1,1

Comments

The 4-almost primes are the numbers that are the product of exactly four (not necessarily distinct) primes.

Links

Table of n, a(n) for n=1..14.

Example

a(1)=88=2*2*2*11;
a(2)=1881=3*3*11*19;
a(3)=218812=2*2*11*4973.

Mathematica

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

Crossrefs

Cf. A014613, A247483, A247484.

Sequence in context: A235018 A228810 A245954 * A107422 A210006 A194491

Adjacent sequences: A248044 A248045 A248046 * A248048 A248049 A248050

Keyword

nonn,base

Author

Michel Lagneau, Dec 01 2014

Status

approved