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A028986 Palindromes whose sum of divisors is palindromic. 6
1, 2, 3, 4, 5, 7, 333, 17571, 1757571, 1787871, 2249422, 4369634, 5136315, 412727214, 439838934, 518686815, 541626145, 17575757571, 52554845525, 4166253526614, 5136813186315, 5136868686315, 5806270726085, 7359770779537, 172757272757271, 513636363636315 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(39) >= 10^18. - Hiroaki Yamanouchi, Sep 27 2014

Intersection of A002113 and of A028980. - Michel Marcus, Apr 06 2015

LINKS

Hiroaki Yamanouchi, Table of n, a(n) for n = 1..38

P. De Geest, World!Of Numbers

MATHEMATICA

palQ[n_]:=Reverse[x=IntegerDigits[n]]==x; t={}; Do[If[palQ[n] && palQ[DivisorSigma[1, n]], AppendTo[t, n]], {n, 5.2*10^6}]; t (* Jayanta Basu, May 17 2013 *)

PROG

(PARI) a(n)=my(d, i, r); r=vector(#digits(n-10^(#digits(n\11)))+#digits(n\11)); n=n-10^(#digits(n\11)); d=digits(n); for(i=1, #d, r[i]=d[i]; r[#r+1-i]=d[i]); sum(i=1, #r, 10^(#r-i)*r[i]) \\ David A. Corneth in A002113, Jun 06 2014

pal(n)=d=digits(n); Vecrev(d)==d

for(n=2, 10^5, if(pal(sigma(a(n))), print1(a(n), ", "))) \\ Derek Orr, Apr 05 2015

CROSSREFS

Cf. A002113 (palindromes), A028980 (sigma(n) is a palindrome).

Sequence in context: A277217 A259384 A285888 * A327324 A063948 A113929

Adjacent sequences:  A028983 A028984 A028985 * A028987 A028988 A028989

KEYWORD

nonn,base

AUTHOR

Patrick De Geest

EXTENSIONS

a(18)-a(24) from Donovan Johnson, Apr 19 2010

a(25)-a(26) from Donovan Johnson, Jun 16 2011

STATUS

approved

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Last modified July 28 14:19 EDT 2021. Contains 346335 sequences. (Running on oeis4.)