A160218 - OEIS

A160218

Index at which n-th prime occurs in A160256, or -1 if the prime never occurs.

2, 3, 14, 20, 32, 301, 1065

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OFFSET

1,1

COMMENTS

A160256(a(n))=A000040(n) if and only if both Conjectures 1 and 2 are true:

Conjecture 1: Primes occur in A160256 in increasing order.

Conjecture 2: All primes occur in A160256.

Conjecture 3: Except for A160256(4)=4, the least positive integer which does not occur in A160256 up to a given index is always a prime (and thus of the form A160256(a(k)) for some k).

Conjecture 4: A160256(a(n)) is always the least positive integer which did not occur earlier in A160256.

LINKS

Table of n, a(n) for n=1..7.

PROG

(PARI) list_A160218(n)={ my(a1=1, a2=1, S=[]); until( isprime(a1) & !print1(#S, ", ") & !n--, for( a=1, 9e9, a*a1%a2 & next; setsearch(S, a) & next; a2=a1; S=setunion(S, Set(a1=a)); /*print1(a", "); */ next(2)); error); vecsort(eval(S)) }

CROSSREFS

Cf. A160256, A151413.

Sequence in context: A284928 A374232 A294405 * A208983 A337609 A081615

Adjacent sequences: A160215 A160216 A160217 * A160219 A160220 A160221

KEYWORD

hard,more,nonn

AUTHOR

M. F. Hasler, May 06 2009

EXTENSIONS

Edited by N. J. A. Sloane, May 16 2009

STATUS

approved