The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A280354

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A280354

Numbers n such that (i) number of divisors of n equals number of divisors of digit reversal of n, (ii) sum of divisors of n equals sum of divisors of digit reversal of n, and (iii) n is not a palindrome.
(history; published version)

#18 by N. J. A. Sloane at Tue Mar 07 00:27:22 EST 2017

STATUS

editing

approved

#17 by N. J. A. Sloane at Tue Mar 07 00:27:06 EST 2017

NAME

Numbers n such that (i) number of divisors of n equals number of divisors of digit reversal of n, (ii) sum of divisors of n equals sum of divisors of digit reversal of n , and (iii) n is not a palindrome.

STATUS

approved

editing

Discussion

Tue Mar 07

00:27

N. J. A. Sloane: Rewrote definition to make it clearer

#16 by N. J. A. Sloane at Tue Mar 07 00:26:40 EST 2017

STATUS

editing

approved

#15 by N. J. A. Sloane at Tue Mar 07 00:26:38 EST 2017

NAME

Numbers n such that (i) number of divisors and sum of divisors of n equals number of divisors and of digit reversal of n, (ii) sum of divisors of n equals sum of divisors of digit reversal of n and (iii) n is not a nonpalindromic numberpalindrome.

STATUS

proposed

editing

#14 by Alonso del Arte at Mon Mar 06 16:24:33 EST 2017

STATUS

editing

proposed

#13 by Alonso del Arte at Mon Mar 06 16:23:33 EST 2017

EXAMPLE

1561 is in the sequence because 1561 has 4 divisors {1, 7, 223, 1561}, 1 + 7 + 223 + 1561 = 1792 and 1651 has 4 divisors {1, 13, 127, 1651}, 1 + 13 + 127 + 1651 = 1792.

MATHEMATICA

Select[Range[1500000], !PalindromeQ[#1] && DivisorSigma[0, #1] == DivisorSigma[0, FromDigits[Reverse[IntegerDigits[#1]]]] && DivisorSigma[1, #1] == DivisorSigma[1, FromDigits[Reverse[IntegerDigits[#1]]]] & ]

FromDigits[Reverse[IntegerDigits[#1]]]] & ]

STATUS

proposed

editing

#12 by Indranil Ghosh at Mon Mar 06 16:20:53 EST 2017

STATUS

editing

proposed

#11 by Indranil Ghosh at Mon Mar 06 16:20:14 EST 2017

PROG

isok(n) = n != R(n) && sigmanumdiv(n, 0) == sigmanumdiv(R(n), 0) && sigma(n, 1) == sigma(R(n), 1);

for(n=1561, 1473302, if(isok(n), print1(n, ", "))) \\ Indranil Ghosh, Mar 06 2017

STATUS

proposed

editing

Discussion

Mon Mar 06

16:20

Indranil Ghosh: Yes, Edited, @Michel.

#10 by Indranil Ghosh at Mon Mar 06 15:48:01 EST 2017

STATUS

editing

proposed

Discussion

Mon Mar 06

16:06

Michel Marcus: You could use numdiv(n) to get a shorter line, if you will

16:07

Michel Marcus: And simply sigma(n) rather than sigma(n,1)

#9 by Indranil Ghosh at Mon Mar 06 15:47:25 EST 2017

PROG

(PARI) R(n) = eval(concat(Vecrev(Str(n))));

R(n) = eval(concat(Vecrev(Str(n))));

STATUS

proposed

editing