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A071393 Reverse of largest prime factor of n = smallest prime factor of n+1; a(1)=1. 1
1, 558, 1456, 2170, 2976, 4680, 5328, 6816, 7098, 7812, 9796, 10230, 13192, 13578, 14058, 14260, 15066, 19096, 22320, 26128, 26350, 28542, 28768, 30600, 32338, 33696, 36828, 38440, 40612, 40950, 50268, 53946, 57510, 58590, 62196, 64750 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..1000

EXAMPLE

13578 is here since 13578 = 2.3.31.'73' and 13579 = '37'.367.

MAPLE

revdigs:= proc(n) option remember; local L, i;

  L:= convert(n, base, 10);

  add(L[-i]*10^(i-1), i=1..nops(L));

end proc:

filter:= proc(n) local p;

  p:= revdigs(max(numtheory:-factorset(n)));

  isprime(p) and p = min(numtheory:-factorset(n+1))

end proc:

filter(1):= true:

select(filter, [$1..10000]); # Robert Israel, Apr 02 2020

MATHEMATICA

Join[{1}, Select[Range[65000], IntegerReverse[FactorInteger[#][[-1, 1]]] == FactorInteger[ #+1][[1, 1]]&]] (* Harvey P. Dale, Mar 29 2018 *)

CROSSREFS

Cf. A006530, A020639.

Sequence in context: A260066 A105979 A183779 * A253290 A206123 A253160

Adjacent sequences:  A071390 A071391 A071392 * A071394 A071395 A071396

KEYWORD

base,nonn

AUTHOR

Jason Earls, Jun 12 2002

STATUS

approved

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Last modified July 11 03:56 EDT 2020. Contains 335609 sequences. (Running on oeis4.)