A058849 Sum of odd composites up to n is palindromic.

9, 55, 99, 215, 357, 663, 3725, 6321, 26999, 191363, 675861, 4073533, 4180943, 5540147, 6531789, 400974175, 4248550291, 6224149881, 17109266357, 38023877981, 55995454633, 62836534343, 212955815417

Offset: 1

Author

Patrick De Geest, Dec 15 2000

Keywords

• nonn
• base
• more

Comments

Sequence is 9 + 15 + 21 + 25 + 27 + 33 + ... + n.

Links

• P. De Geest, Palindromic Sums

Crossrefs

Cf. A058848, A058850.

Programs

Maple

nextA071904 := proc(n) local a ; a := n + 2 - ((n+1) mod 2); while isprime(a) do a := a+2 ; od ; RETURN(a) ; end: isA002113 := proc(n) local drev,i ; drev := convert(n,base,10) ; for i from 1 to nops(drev)/2 do if op(i,drev) <> op(-i,drev) then RETURN(false) ; fi ; od ; RETURN(true) ; end: nextA058844 := proc(n,nsum) local a, asum ; a := nextA071904(n) ; asum := nsum+a ; while not isA002113(asum) do a := nextA071904(a) ; asum := asum+a ; od ; RETURN([a, asum]) ; end: n := 9 ; nsum := 9 ; nnsum := [n,nsum] ; for i from 1 to 40 do print(op(1,nnsum)) ; nnsum := nextA058844(op(1,nnsum),op(2,nnsum)) ; od : # R. J. Mathar, Jan 29 2007

Formula

Sum_{i=1..j} A071904(i) = A002113(k) for A071904(j) = n and some k. - R. J. Mathar, Jan 29 2007

Extensions

a(20) from Donovan Johnson, Sep 01 2012

a(21)-a(23) from Chai Wah Wu, Dec 06 2019