A082518 Palindromic primes whose digital root equals their middle digits.

919, 929, 18181, 18481, 36263, 36563, 72227, 72727, 90709, 1082801, 1085801, 1175711, 1177711, 1178711, 1262621, 1268621, 1444441, 1447441, 1532351, 1535351, 1628261, 1712171, 1714171, 1802081, 1805081, 1895981, 1981891

Offset

1,1

Comments

All terms must have an odd number of digits. - Harvey P. Dale, Jun 13 2015

Links

Harvey P. Dale, Table of n, a(n) for n = 1..100

Example

1895981 is in the sequence because digital root rho(1895981)=rho(1+8+9+5+9+8+1)=rho(41)=4+1=5, which is the middle digit of 1895981.

Mathematica

ppdrQ[n_]:=Module[{idn=IntegerDigits[n]}, OddQ[Length[idn]]&&idn== Reverse[ idn] && NestWhile[Total[IntegerDigits[#]]&, n, #>9&] == idn[[(Length[ idn]+1)/2]]]; Select[Prime[Range[5, 150000]], ppdrQ] (* Harvey P. Dale, Jun 13 2015 *)

Crossrefs

Cf. A002385.

Sequence in context: A221113 A062335 A179673 * A128375 A068689 A088284

Adjacent sequences: A082515 A082516 A082517 * A082519 A082520 A082521

Keyword

base,nonn

Author

Lekraj Beedassy, Apr 30 2003

Extensions

Corrected by Don Reble and T. D. Noe, Nov 15 2006

Status

approved