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A247484 a(1)=8; for n>=1, a(n+1) is the smallest palindromic 3-almost prime with a(n) as a central substring. 2
8, 282, 52825, 4528254, 145282541, 2214528254122, 122145282541221, 51221452825412215, 7512214528254122157, 15751221452825412215751, 7157512214528254122157517, 371575122145282541221575173, 93715751221452825412215751739, 3937157512214528254122157517393 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

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

EXAMPLE

a(1) = 8 = 2*2*2;

a(2) = 282 = 2*3*47;

a(3) = 52825 = 5*5*2113;

a(4) = 4528254 = 2*3*754709.

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

CROSSREFS

Cf. A014612, A247483.

Sequence in context: A226346 A217488 A332128 * A136364 A089670 A221612

Adjacent sequences:  A247481 A247482 A247483 * A247485 A247486 A247487

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Dec 01 2014

STATUS

approved

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Last modified February 23 00:28 EST 2020. Contains 332157 sequences. (Running on oeis4.)