A098767 Deficient numbers whose reversal is also a deficient number.

1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19, 22, 23, 25, 26, 29, 31, 32, 33, 34, 35, 37, 38, 39, 41, 43, 44, 46, 47, 49, 50, 51, 52, 53, 55, 57, 58, 59, 61, 62, 64, 67, 68, 71, 73, 74, 75, 76, 77, 79, 83, 85, 86, 89, 91, 92, 93, 94, 95, 97, 98, 99, 101, 103, 105, 106

Offset

1,2

Links

Ivan Neretin, Table of n, a(n) for n = 1..10000

Example

a(12)=14 because 14 and reverse of 14, i.e., 41, are deficient numbers.
a(13)=15 because 15 is a deficient number which on reversing its digits also gives a deficient number, i.e., 51.

Mathematica

Select[Range@106, DivisorSigma[1, #] < 2 # && DivisorSigma[1, n = FromDigits@Reverse@IntegerDigits@#] < 2 n &] (* Ivan Neretin, Dec 19 2015 *)

Prog

(PARI) isdefic(n) = (sigma(n) < 2*n);
isok(n) = isdefic(n) && isdefic(eval(concat(Vecrev(Str(n))))); \\ Michel Marcus, Dec 20 2015

Crossrefs

Cf. A005100.

Sequence in context: A051772 A049093 A098901 * A333559 A153381 A307750

Adjacent sequences: A098764 A098765 A098766 * A098768 A098769 A098770

Keyword

easy,nonn,base

Author

Shyam Sunder Gupta, Oct 02 2004

Extensions

Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Jun 11 2007

Status

approved