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A087400 Primes p such that p+2 is a piptorial number. Also numbers such that A080696(n)- 2 is prime. 0
13, 163, 2803, 3565153, 210344143, 86915972211813115391953, 4419764102942908730796303703, 114681479899746991802547357477494803 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Piptorial numbers are the partial products of prime-indexed primes. Sum of reciprocals = 0.08341509210884323904648676616...

LINKS

Table of n, a(n) for n=1..8.

FORMULA

(Product of first four pips) - 2 = 3*5*11*17 - 2 = 2805 - 2 = 2803, which is prime, so 2803 is in the sequence.

PROG

(PARI) piptorial(n) = { s=0; p=1; for(x=1, n, p=p*prime(prime(x)); if(isprime(p-2), print1(p-2", "); s+=1.0/(p-2)) ); print(); print(s) }

CROSSREFS

Cf. A080696.

Sequence in context: A212785 A133180 A090134 * A012828 A119539 A277412

Adjacent sequences:  A087397 A087398 A087399 * A087401 A087402 A087403

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Oct 21 2003

STATUS

approved

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Last modified August 12 15:02 EDT 2022. Contains 356077 sequences. (Running on oeis4.)