A246808 Palindromic terms of the sequence A245317.

2112, 4803443084, 6992662996, 180461164081, 214591195412, 409473374904, 563715517365, 4163019339103614, 1050417996997140501

Offset: 1

Author

Jahangeer Kholdi, Sep 17 2014

Keywords

• nonn
• base
• more

Comments

For each n, A100414(n).reversal(A100414(n)) is in the sequence, where dot denotes concatenation. What is the first term of the sequence which is not of the above form?

a(9) <= 253385633342243336583352 and a(10) <= 661494322636636223494166.

a(9) = A245317(997140501) = 1050417996997140501 is the smallest term of the sequence which is not of the form A100414(n).reversal(A100414(n)). 253385633342243336583352 and 661494322636636223494166 are two consecutive terms of the sequence. - Farideh Firoozbakht, Sep 23 2014

Crossrefs

Cf. A002808, A004086, A100414, A245317.

Programs

Mathematica

h[n_]:=If[!PrimeQ[n],FromDigits[Flatten[{IntegerDigits[n],IntegerDigits[n-PrimePi[n]-1]}]]];Do[a=h[n];If[!PrimeQ[n]&&FromDigits[Reverse[IntegerDigits[a]]]==a,Print[a]],{n,100000000}]

Formula

For n<9, a(n) = A100414(n).reversal(A100414(n)).

Extensions

a(9) from Farideh Firoozbakht, Sep 23 2014