A100003
Prime numbers p such that the concatenation of all odd primes up through p in decreasing order is prime.
Original entry on oeis.org
3, 5, 17, 89, 383, 8831
Offset: 1
17 is in the sequence because 17.13.11.7.5.3 is prime (dot between numbers means concatenation).
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Do[If[PrimeQ[(v={};Do[v=Join[v, IntegerDigits[Prime[n-j+1]]], {j, n-1}];FromDigits[v])], Print[Prime[n]]], {n, 2, 4413}]
Prime[#]&/@Select[Range[100],PrimeQ[FromDigits[Flatten[IntegerDigits/@ Prime[Range[#,2,-1]]]]]&] (* To generate a(6) increase the Range by 1000, but the program will run a long time. *) (* Harvey P. Dale, Nov 27 2015 *)
A092447
Concatenate odd primes in decreasing order.
Original entry on oeis.org
3, 53, 753, 11753, 1311753, 171311753, 19171311753, 2319171311753, 292319171311753, 31292319171311753, 3731292319171311753, 413731292319171311753, 43413731292319171311753, 4743413731292319171311753, 534743413731292319171311753, 59534743413731292319171311753
Offset: 1
Micha Fleuren (michafleuren(AT)hotmail.com), Mar 24 2004
- Andrew Howroyd, Table of n, a(n) for n = 1..100
- M. Fleuren, Smarandache Back Concatenated Odd Primes
- H. Marimutha, Smarandache Concatenated Type Sequences, Bulletin of Pure and Applied Sciences, Vol. 16 E(No.2), 1997; p. 225-226.
- F. Smarandache, Collected papers, Vol. II, University of Kishinev, 1997.
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Table[FromDigits[Flatten[IntegerDigits/@Reverse[Prime[Range[2,n]]]]],{n,2,21}] (* Harvey P. Dale, Mar 01 2023 *)
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a(n)={fromdigits(concat([digits(k) | k<-Vecrev(primes(n+1))[1..n]]))} \\ Andrew Howroyd, Feb 12 2020
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