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 A260801 Primes p such that A008908(p) is also prime. 0
 2, 7, 17, 29, 31, 71, 89, 107, 113, 127, 131, 157, 181, 223, 239, 263, 271, 277, 281, 283, 313, 337, 379, 409, 419, 421, 431, 503, 547, 571, 577, 691, 701, 727, 757, 809, 821, 857, 883, 947, 953, 971, 1031, 1109, 1129, 1153, 1163, 1231, 1283, 1291, 1327, 1361, 1447, 1487, 1531, 1559, 1567, 1583 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..58. Index entries for sequences related to 3x+1 (or Collatz) problem EXAMPLE 7 is prime and A008908(7) is 17, which is also prime. Therefore, 7 is in the sequence. MATHEMATICA collatz[n_]:=If[EvenQ[n], n/2, 3*n+1]; seq[n_]:=Length[NestWhileList[collatz, n, #!= 1&]] Select[Flatten[Position[seq/@Range[7!], _?PrimeQ]], PrimeQ] PROG (PARI) T(n)=c=0; while(n!=1, if(n%2, n=3*n+1; c++); if(!(n%2), n=n/2; c++)); c+1 forprime(p=1, 10^3, if(isprime(T(p)), print1(p, ", "))) \\ Derek Orr, Aug 27 2015 CROSSREFS Cf. A008908. Sequence in context: A049582 A220273 A276698 * A031377 A019357 A024920 Adjacent sequences: A260798 A260799 A260800 * A260802 A260803 A260804 KEYWORD easy,nonn AUTHOR Ivan N. Ianakiev, Jul 31 2015 STATUS approved

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Last modified June 10 17:16 EDT 2023. Contains 363206 sequences. (Running on oeis4.)