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A280427 a(n) is a prime, such that a(n) = p^d-2 where p is a prime and d is the number of digits of p. 1
3, 5, 167, 359, 839, 1367, 1847, 2207, 3719, 5039, 7919, 1295027, 3442949, 9393929, 13997519, 21253931, 49430861, 84604517, 95443991, 237176657, 329939369, 384240581, 487443401, 633839777, 904231061, 1078193566319, 1427186233199, 1556727840719, 1985193642959 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These numbers (proved for all p < 500) are a subset of A007528. For all even p, such numbers are a subset of A007528. The sequence is a subset of all numbers f(i) such that f(i) = i^d-2 (d - number of digits of integer i) and f(i) is a prime: e.g., f(15) is prime while f(15) = 15^2-2 = 223.

LINKS

Table of n, a(n) for n=1..29.

FORMULA

a(n) = p^d-2, a(n) is prime, p is a prime and d is the number of digits of p.

EXAMPLE

If p=5, then d=1 and a(1)=3; if p=7, then d=1 and a(2)=5; if p=13, then d=2 and a(3)=167; etc.

MAPLE

P:=proc(q) local a, b; a:=ithprime(q); b:=a^(ilog10(a)+1)-2;

if isprime(b) then b; fi; end: seq(P(k), k=1..1000); # Paolo P. Lava, Jan 04 2017

MATHEMATICA

Select[Array[#^IntegerLength@ # - 2 &@ Prime@ # &, 200], PrimeQ] (* Michael De Vlieger, Jan 03 2017 *)

CROSSREFS

Cf. A007528.

Sequence in context: A240125 A108013 A087307 * A038535 A090953 A092947

Adjacent sequences:  A280424 A280425 A280426 * A280428 A280429 A280430

KEYWORD

nonn,base

AUTHOR

Sergey Pavlov, Jan 02 2017

EXTENSIONS

More terms from Michael De Vlieger, Jan 03 2017

STATUS

approved

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Last modified September 18 20:19 EDT 2020. Contains 337173 sequences. (Running on oeis4.)