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A247483 a(1)=4; for n>=1, a(n+1) is the smallest palindromic semiprime with a(n) as a central substring. 3
4, 141, 41414, 1414141, 314141413, 33141414133, 3331414141333, 14333141414133341, 121433314141413334121, 1012143331414141333412101, 17101214333141414133341210171, 3171012143331414141333412101713, 19317101214333141414133341210171391 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..13.

EXAMPLE

a(1) = 4 = 2*2;

a(2) = 141 = 3*47;

a(3) = 41414 = 2*20707;

a(4) = 1414141 = 43*32887.

MATHEMATICA

d[n_] := IntegerDigits[n]; t = {x = 4}; Do[i = 1; While[!PrimeOmega[y = FromDigits[Flatten[{z = d[i], d[x], Reverse[z]}]]]==2, i++]; AppendTo[t, x = y], {n, 12}]; t

CROSSREFS

Cf. A001358, A053600.

Sequence in context: A299061 A299722 A210831 * A293752 A299833 A231949

Adjacent sequences:  A247480 A247481 A247482 * A247484 A247485 A247486

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Dec 01 2014

STATUS

approved

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Last modified February 20 22:47 EST 2020. Contains 332086 sequences. (Running on oeis4.)