A023568 -id:A023568 - cp's OEIS frontend

A023569 Greatest prime divisor of prime(n) - 3.

2, 2, 2, 5, 7, 2, 5, 13, 7, 17, 19, 5, 11, 5, 7, 29, 2, 17, 7, 19, 5, 43, 47, 7, 5, 13, 53, 11, 31, 2, 67, 17, 73, 37, 11, 5, 41, 17, 11, 89, 47, 19, 97, 7, 13, 11, 7, 113, 23, 59, 17, 31, 127, 13, 19, 67, 137, 139, 7, 29, 19, 11, 31, 157, 41, 167, 43, 173, 7, 89

Offset: 3

Clark Kimberling

nonn

a(n) = 2 if prime(n) is in A057733. - Robert Israel, Dec 28 2015

Robert Israel, Table of n, a(n) for n = 3..10000

Cf. A023568, A057733.

seq(max(numtheory:-factorset(ithprime(i)-3)), i=3..100); # Robert Israel, Dec 28 2015

Table[FactorInteger[Prime[n] - 3] [[-1, 1]], {n, 3, 100}] (* Vincenzo Librandi, Dec 29 2015 *)

a(n) = vecmax(factor(prime(n)-3)[,1]); \\ Michel Marcus, Dec 29 2015

Corrected by Robert Israel, Dec 29 2015

A023516 Number of distinct prime divisors of prime(n)*prime(n-1) - 1.

Original entry on oeis.org

0, 1, 2, 2, 2, 2, 3, 3, 2, 3, 2, 3, 2, 2, 3, 4, 3, 3, 3, 3, 2, 3, 3, 3, 3, 3, 3, 4, 3, 2, 4, 2, 3, 2, 4, 3, 3, 4, 3, 4, 4, 3, 3, 3, 3, 3, 3, 3, 3, 4, 2, 3, 3, 4, 4, 4, 4, 4, 3, 4, 2, 3, 4, 2, 4, 4, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 4, 3, 2, 4

Offset: 1

Clark Kimberling

nonn

This is taking prime(0)=1 (see first comment in A023515). - Vincenzo Librandi, Apr 27 2019

Vincenzo Librandi, Table of n, a(n) for n = 1..10000

Cf. A023515, A023524, A023568, A023575, A023582, A023589.

[#PrimeDivisors(NthPrime(n)*(NthPrime(n-1))-1): n in [1..100]]; // Vincenzo Librandi, Apr 27 2019

0,seq(nops(numtheory:-factorset(ithprime(n)*ithprime(n-1)-1)),n=2..120); # Muniru A Asiru, Apr 29 2019

Prepend[Table[PrimeNu[Prime[n] Prime[n-1] - 1], {n, 2, 80}],0] (* Vincenzo Librandi, Apr 27 2019 *)

a(n) = if (n==1, 0, omega(prime(n)*prime(n-1) - 1)); \\ Michel Marcus, Apr 30 2019

a(n) = A001221(A023515(n)).

cp's OEIS Frontend

A023569 Greatest prime divisor of prime(n) - 3.

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

Maple

Mathematica

PARI

Extensions