A258581 -id:A258581 - cp's OEIS frontend

A260218 a(1) = 2; for n > 1 if n is even a(n) = spf(1 + Product_{odd m,m

2, 3, 2, 5, 2, 3, 2, 17, 2, 3, 2, 5, 2, 3, 2, 257, 2, 3, 2, 5, 2, 3, 2, 17, 2, 3, 2, 5, 2, 3, 2, 65537, 2, 3, 2, 5, 2, 3, 2, 17, 2, 3, 2, 5, 2, 3, 2, 97, 2, 3, 2, 5, 2, 3, 2, 17, 2, 3, 2, 5, 2, 3, 2, 641, 2, 3, 2, 5, 2, 3, 2, 17, 2, 3, 2, 5, 2, 3

Offset: 1

Anders Hellström, Jul 19 2015

Antti Karttunen, Table of n, a(n) for n = 1..255

Cf. A000945, A005265, A007978, A053669, A075019, A258581.

f[n_] := Block[{a = {2}, k, m}, Do[If[EvenQ@ k, AppendTo[a, FactorInteger[Product[a[[m]], {m, 1, k - 1, 2}] + 1][[1, 1]]], AppendTo[a, FactorInteger[Product[a[[m]], {m, 2, k - 1, 2}] + 1][[1, 1]]]], {k, 2, n}]; a]; f@ 80 (* Michael De Vlieger, Jul 20 2015 *)

spf(n)=factor(n)[1, 1]
first(m)=my(v=vector(m), i, odd=2, even=1); v[1]=2; for(i=2, m, if(i%2==0, v[i]=spf(odd+1); even*=v[i], v[i]=spf(even+1); odd*=v[i])); v; /* Anders Hellström, Jul 19 2015 */

A020639(n) = if(1==n,n,vecmin(factor(n)[, 1]));
memoA260218 = Map();
A260218(n) = if(1==n,2,if(mapisdefined(memoA260218,n),mapget(memoA260218,n), my(k, m, v = if(!(n%2), k=1; m=1; while(kA260218(k); k += 2); A020639(m+1), k=2; m=1; while(kA260218(k); k += 2); A020639(m+1))); mapput(memoA260218,n,v); (v))); \\ (An incrementally memoized version). Antti Karttunen, Sep 30 2018

It appears that for odd k, a(k) = 2 and for even k, a(k) = A002586(k/2). - Michel Marcus, Jul 20 2015

A260724 a(1) = 2; for n > 1 if n mod 3=0 a(n) = gpf(1 + Product_{m modulo 3=2,m

Original entry on oeis.org

2, 3, 2, 7, 5, 2, 31, 3, 109, 13, 97, 83, 8731, 461, 3078769, 574933, 206179, 510583, 5153873111, 1900169, 372828179, 4032506435771041, 3445362972116384083, 49898596950715368948711529590337583, 54176564592185030069557382121821

Offset: 1

Anders Hellström, Jul 30 2015

nonn

Anders Hellström, Table of n, a(n) for n = 1..27

Cf. A258581

gpf(n)=my(v=factor(n)[, 1]); v[#v];
first(m)={my(v=vector(m),one=2,two=2,three=1);v[1]=2;for(i=2, m,if(i%3===0,v[i]=gpf(three+1);two*=v[i],if(i%3===1,v[i]=gpf(one+1);three*=v[i],v[i]=gpf(two+1);one*=v[i])));v;}

cp's OEIS Frontend

A260218 a(1) = 2; for n > 1 if n is even a(n) = spf(1 + Product_{odd m,m

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A260724 a(1) = 2; for n > 1 if n mod 3=0 a(n) = gpf(1 + Product_{m modulo 3=2,m

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