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A200071
Numbers n such that the sum of the prime distinct divisors of n^2+1 equals 2 times the difference between the largest and the smallest prime divisor.
2
447, 2042, 4942, 8673, 17232, 18321, 38232, 52953, 54468, 54974, 55174, 57229, 66567, 71132, 83071, 101499, 113667, 121206, 133047, 173932, 297907, 325286, 430353, 447131, 656079, 702969, 842151, 937313, 1061846, 1173886, 1613346, 1721094, 1754679, 1759310
OFFSET
1,1
LINKS
EXAMPLE
447 is a term because the distinct prime divisors of 447^2 + 1 are 2, 5, 13, 29, 53 and their sum, 2 + 5 + 13 + 29 + 53 = 102, equals 2*(53 - 2).
MATHEMATICA
Select[Range[1800000], Plus@@(pl=First/@FactorInteger[#^2+1])/2==pl[[-1]]-pl[[1]]&]
spddQ[n_]:=Module[{fi=FactorInteger[n^2+1][[All, 1]]}, Total[fi] == 2*(Last[ fi]-First[fi])]; Select[Range[176*10^4], spddQ] (* Harvey P. Dale, Jan 12 2019 *)
CROSSREFS
Cf. A200070.
Sequence in context: A139230 A221506 A065576 * A203960 A147628 A153486
KEYWORD
nonn
AUTHOR
Michel Lagneau, Nov 13 2011
STATUS
approved