A261493 Palindromes that are concatenation of palindromic prime numbers in increasing order up to the n-th and then in decreasing order.
2, 232, 23532, 2357532, 2357117532, 235711101117532, 235711101131101117532, 235711101131151131101117532, 235711101131151181151131101117532, 235711101131151181191181151131101117532, 235711101131151181191313191181151131101117532
Offset: 1
Examples
For n=6, the first 6 palindromic primes are 2,3,5,7,11,101. Relevant subsequence that produce a(6) is 2,3,5,7,11,101,11,7,5,3,2. Concatenation of items with that order determines a(6) = 235711101117532.
Programs
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Mathematica
palQ[n_] := Reverse[idn = IntegerDigits@ n] == idn; s = Select[ Prime@ Range@ 1000, palQ]; f[n_] := FromDigits@ Flatten[ IntegerDigits@# & /@ Join[ Take[s, n], Reverse@ Take[s, n - 1]]]; Array[f, 11] (* Robert G. Wilson v, Aug 24 2015 *)
Comments