A225720 Composite squarefree numbers n such that p+10 divides n-10 for each prime p dividing n.

10, 79222, 206965, 784090, 1673122, 2227123, 4798090, 5202571, 9196330, 13146715, 15015430, 18213595, 19342333, 21735010, 27907435, 28234018, 28240090, 37394146, 38710990, 53990695, 54772453, 70646509, 79671826, 89678830, 107251990, 114572545, 115005187, 137245690

Offset

1,1

Links

Table of n, a(n) for n=1..28.

Example

Prime factors of 2227123 are 19, 251 and 467. We have that (2227123-10)/(19+10) = 76797, (2227123-10)/(251+10) = 8533 and (2227123-10)/(467+10) = 4669.

Maple

with(numtheory); A225720:=proc(i, j) local c, d, n, ok, p, t;
for n from 2 to i do if not isprime(n) then p:=ifactors(n)[2]; ok:=1;
for d from 1 to nops(p) do if p[d][2]>1 or p[d][1]=j then ok:=0; break; fi;
if  not type((n+j)/(p[d][1]-j), integer) then ok:=0; break; fi; od;
if ok=1 then print(n); fi; fi; od; end: A225720(10^9, -10);

Prog

(PARI) is(n, f=factor(n))=if(#f[, 2]<2 || vecmax(f[, 2])>1, return(0)); for(i=1, #f~, if((n-10)%(f[i, 1]+10), return(0))); 1 \\ Charles R Greathouse IV, Nov 05 2017

Crossrefs

Cf. A208728, A225702-A225719.

Sequence in context: A048832 A225070 A115673 * A013792 A139106 A307927

Adjacent sequences: A225717 A225718 A225719 * A225721 A225722 A225723

Keyword

nonn

Author

Paolo P. Lava, May 13 2013

Extensions

a(20)-a(27) from Donovan Johnson, Nov 15 2013

a(28) from Charles R Greathouse IV, Nov 05 2017

Status

approved