A071393 Reverse of largest prime factor of n = smallest prime factor of n+1; a(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

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: A183779 A342825 A340712 * A352350 A253290 A206123

Adjacent sequences: A071390 A071391 A071392 * A071394 A071395 A071396

Keyword

base,nonn

Author

Jason Earls, Jun 12 2002

Status

approved