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A248856 Numbers n such that n + pi(n) is a power of 10. 1
1, 853, 91182, 926756, 9374193, 94535668, 951496285, 9563906973, 963706466000, 9665127969899, 96891533076641, 970995550452370, 9728143518403637, 97441817594570206, 975843062833251485, 9771174122943813068 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that pi(n) equals 10^ceiling(log(10,n)) - n.

853 is the only known prime term of the sequence. If n is a prime term of the sequence and m = pi(n) then prime(m) + m is a power of 10. So 147 = pi(853) is the only known number m such that prime(m) + m is a power of 10. What is the next such number?

For each number n there exists at most one n-digit term.

a(11) = 96891533076641 is also prime. - Chai Wah Wu, May 25 2018

LINKS

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

EXAMPLE

pi(96891533076641) + 96891533076641 = 10^14 so 96891533076641 is in the sequence.

MATHEMATICA

Select[Range[1000], IntegerQ[Log[10, # + PrimePi[#]]] &] (* Alonso del Arte, Dec 31 2014 *)

PROG

(PARI) for(n=1, 10^3, s=digits(n+primepi(n)-1); if(s==[]||vecmin(s)==9, print1(n, ", "))) \\ Derek Orr, Jan 02 2015

CROSSREFS

Cf. A000720, A244440, A248854.

Sequence in context: A234539 A251148 A127593 * A251050 A085323 A185639

Adjacent sequences:  A248853 A248854 A248855 * A248857 A248858 A248859

KEYWORD

nonn,hard

AUTHOR

Farideh Firoozbakht, Dec 31 2014

EXTENSIONS

a(12)-a(16) from Chai Wah Wu, May 25 2018

STATUS

approved

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Last modified September 16 23:53 EDT 2021. Contains 347477 sequences. (Running on oeis4.)