A260681 - OEIS

A260681

a(1) = a(2) = 1; a(n) = a(n-1) + gpf(1 + Product_{k = 1..n - 2} a(k)), where gpf means "greatest prime factor" (A006530).

1, 1, 3, 5, 7, 9, 62, 105, 4612, 477839, 5221660, 120695273, 13517914794489425446, 949763730038903507583, 805993247839619614799176726719363512, 2572332284084802308827712032135882716710570503279953274299454873

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

LINKS

Table of n, a(n) for n=1..16.

EXAMPLE

a(3) = a(2) + gpf(1 + a(1)) = 1 + gpf(1 + 1) = 1 + 2 = 3.

a(4) = a(3) + gpf(1 + a(1) * a(2)) = 3 + gpf(1 + 1 * 1) = 3 + 2 = 5.

a(5) = a(4) + gpf(1 + a(1) * a(2) * a(3)) = 5 + gpf(1 + 1 * 1 * 3) = 5 + 2 = 7.

PROG

(PARI) gpf(n)=my(f=factor(n)[, 1]); f[#f];

a(n)=if(n>2, a(n-1)+gpf(1+prod(i=1, n-2, a(i))), 1)

first(m)=my(v=vector(m)); v[1]=1; v[2]=1; for(i=3, m, v[i]=v[i-1]+gpf(1+prod(k=1, i-2, v[k]))); v

CROSSREFS

Cf. A006530, A078695.

Sequence in context: A007632 A117996 A234524 * A092046 A228328 A085951

Adjacent sequences: A260678 A260679 A260680 * A260682 A260683 A260684

KEYWORD

nonn

AUTHOR

Anders Hellström, Nov 22 2015

STATUS

approved