A083660 -id:A083660 - cp's OEIS frontend

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

14, 15, 23, 25, 37, 39, 44, 54, 55, 70, 79, 88, 90, 98, 102, 118, 123, 134, 136, 143, 144, 151, 174, 182, 202, 209, 215, 226, 230, 232, 245, 254, 256, 257, 258, 262, 264, 267, 272, 284, 287, 297, 300

Offset: 1

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Farideh Firoozbakht, Jun 27 2003

easy
base
nonn

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.

			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.

Cf. A083660, A032702.

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

cp's OEIS Frontend

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

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