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 A084429 Integers m such that the base-10 digit concatenation 4//m//3//m//2//m//1 is prime. 0

%I #16 Apr 17 2016 09:01:11

%S 14,15,23,25,37,39,44,54,55,70,79,88,90,98,102,118,123,134,136,143,

%T 144,151,174,182,202,209,215,226,230,232,245,254,256,257,258,262,264,

%U 267,272,284,287,297,300

%N Integers m such that the base-10 digit concatenation 4//m//3//m//2//m//1 is prime.

%C I called this sequence f4i and defined similar sequences {fni} in the comments in A083660: fni(m) is the m-th nonnegative integer k such that the concatenation fi(n, k) = n//k//n-1//k// ...//3//k//2//k//1 is prime. By this definition f2i = A032702.

%e a(3)=23 because 23 is the third nonnegative integer m such that fi(4,m)= (fi(4,23)=4 // 23 // 3 // 23 // 2 // 23 //1=4233232231 is prime.

%t Do[If[PrimeQ[FromDigits[Join[{4}, IntegerDigits[n], {3}, IntegerDigits[n], {2}, IntegerDigits[n], {1}]]], v=Insert[v, n, -1]], {n, 300}]; v

%Y Cf. A083660, A032702.

%K easy,base,nonn

%O 1,1

%A _Farideh Firoozbakht_, Jun 27 2003

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Last modified June 6 15:09 EDT 2023. Contains 363147 sequences. (Running on oeis4.)